Huseng wrote:For instance, in basic Abhidharma there are eighteen compositional elements for cognition (aṣṭādaśa-dhātavaḥ). They include the six sense faculties (eye, ear, nose, tongue, body, and mind), their six corresponding objects (sight, hearing, smell, taste, touch and ideation) and the resulting six consciousnesses (vijñāna).
Beyond this there are no other consciousnesses or mind.
Well, there are grounds to dispute that. The exact status of
citta is rather ambiguous in the early texts. There is one school of thought that would subscribe to that view, but there are others. For instance there is the verse on 'luminous mind' in the Pali texts, which is often seen (i.e, by Harvey) as the pre-cursor to the later mind-only schools.
"Luminous, monks, is the mind. And it is defiled by incoming defilements."
"Luminous, monks, is the mind. And it is freed from incoming defilements."
"Luminous, monks, is the mind. And it is defiled by incoming defilements.
The uninstructed run-of-the-mill person doesn't discern that as it actually is present, which is why I tell you that — for the uninstructed run-of-the-mill person — there is no development of the mind."
"Luminous, monks, is the mind. And it is freed from incoming defilements. The well-instructed disciple of the noble ones discerns that as it actually is present, which is why I tell you that — for the well-instructed disciple of the noble ones — there is development of the mind."
(Pabhassara Sutta)
(It is instructive that Ven Thanissaro's commentary on that Sutta in Access to Insight really cannot come to terms with the notion, in my view,
precisely because it seems to contradict the standard abhidhamma account.)
As for whether there is or is not a kind of 'transcendent mind', consider the following:
Then Ven. Maha Kotthita went to Ven. Sariputta and, on arrival, exchanged courteous greetings with him. After an exchange of friendly greetings & courtesies, he sat to one side. As he was sitting there, he said to Ven. Sariputta, "With the remainderless stopping & fading of the six contact-media [vision, hearing, smell, taste, touch, & intellection] is it the case that there is anything else?"
[Sariputta:] "Don't say that, my friend."
[Maha Kotthita:] "With the remainderless stopping & fading of the six contact-media, is it the case that there is not anything else?"
[Sariputta:] "Don't say that, my friend."
[Maha Kotthita:] "...is it the case that there both is & is not anything else?"
[Sariputta:] "Don't say that, my friend."
[Maha Kotthita:] "...is it the case that there neither is nor is not anything else?"
[Sariputta:] "Don't say that, my friend."
[Maha Kotthita:] "Being asked if, with the remainderless stopping & fading of the six contact-media, there is anything else, you say, 'Don't say that, my friend.' Being asked if ... there is not anything else ... there both is & is not anything else ... there neither is nor is not anything else, you say, 'Don't say that, my friend.' Now, how is the meaning of your words to be understood?"
[Sariputta:] "The statement, 'With the remainderless stopping & fading of the six contact-media [vision, hearing, smell, taste, touch, & intellection] is it the case that there is anything else?' objectifies non-objectification.[1] The statement, '... is it the case that there is not anything else ... is it the case that there both is & is not anything else ... is it the case that there neither is nor is not anything else?' objectifies non-objectification. However far the six contact-media go, that is how far objectification goes. However far objectification goes, that is how far the six contact media go. With the remainderless fading & stopping of the six contact-media, there comes to be the stopping, the allaying of objectification.
(Kotthita Sutta)
The phrase ‘objectifies non-objectification’ is key here. As Thanissaro Bikkhu notes in his commentary, ‘the root of the classifications and perceptions of objectification is the thought, "I am the thinker." This thought forms the motivation for the questions that Ven. Maha Kotthita is presenting here.’ The very action of thinking ‘creates the thinker’. In effect, the questioner is asking, ‘is this something I can experience?’ And to do so, tends towards
eternalism. But I would say that the opposite view, that there is nothing beyond the 'six sense gates', tends towards
nihilism.
Shel wrote:How can a mind develop, or be sustained once developed, without sense data?
Well, I agree it can't be. But we are not talking about
a mind, but Mind. Of course I quite agree that this is a mysterious and elusive concept, which is one reason why it has been dropped from much contemporary discourse. But if you consider, for instance, the Tibetan teaching of the One Mind, here you have a philosophical framework within which Mind is understood as 'self-existent', that is, not dependent on anything else, uncreated and uncaused. But you have to be careful because it ought never be reified into an object (for which, see the above points.)
AND, once again, I find myself in pretty well complete agreement with SteveB's post, above.

He that knows it, knows it not.