Thanks to David for citing a source of this material. Naturally, I had to read it.
As it transpires, the "tract" is a 214 page disquisition on what was known about "mollusks" to the science of 1841. As David notes, that category, at that time, included brachiopods and barnacles.
The booklet is quite a tour de force with diagrams of snail hearts and barnacle anatomy and on and on. I learned from it such diverting items as that the English of the time thought that the ingestion of snails made for fat sheep.
The last 3 pages, as expected, concluded by drawing some apologetic conclusions from the science but, as a piece of literature, it definitely rates as a fairly heavy-duty textbook on the science of "mollusks." Actually, it's a quite impressive summary with considerable detail included.
As to the "inmates", the term seems designed to be an eye-catching title feature rather than a theme of the teaching.