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Show 732 DR. J. E. GRAY ON THE CALYPTRJEIDJE. [June 27, smaller groups, and according to the structure of the mollusca and their teeth and anatomy, the opercula, and the shells. The dealers were at length convinced (as Humphrey had been many years before) that the use of a larger number of genera extended their trade, as it produced a crop of customers (besides those who merely bought shells for their beauty or variety) who purchased the less conspicuous shells for the purpose of obtaining one or more examples of each genus ; and the general students were gradually induced to adopt the improvement. The students of fossil shells seem inclined to lag behind the knowledge of the day. They have some excuse, as fossil shells do not afford them all the means of study to be obtained from recent species; but they might do much more than they have done, and they never can derive all the advantages in geology that the study of the fossil mollusca can afford them until they study their shells with the same attention as has been applied to the recent species, and revise the heterogeneous genera into which they are now grouped. Mr. Searles Wood, long ago, set an example of the right course to be pursued in his paper " O n the Crag Fossils;" but few have followed him. I think that the faith they place in Woodward's ' Manual' is one of the causes of their want of progress. The iconographers, such as Lovell Reeve and Mr. Sowerby, have published illustrated monographs of many genera of shells on the modern system ; but unfortunately they do not seem to think it is enough to figure each species, but they figure even slight varieties under the name of species. This has rendered their works so expensive that they are only to be regarded as works of luxury for the libraries of the rich ; while the number of the varieties they figure, and the want of system in the arrangement of the species, render them very difficult to use by the scientific conchologist. You may almost buy a good collection of shells for the price of these works; and every one would learn more from the shells themselves than from works on them of such an unscientific character. Fam. CALYPTR^ID^E. The shells of Calyptrceidce are peculiar as being spiral shells which have the edge of the mouth so expanded behind as to cover the hinder part of the foot of the animal. The front side of the last whorls of the shell, which lies on the upper surface of the foot, being protected from external injury by this extension of the margin of the mouth of the shell, is thin and polished externally, like the rest of the inner surface of the cavity of the shell, of which it seems to form a part. When we have observed the rationale of the structure, the difference between the two families Calyptrceidce and Capulidee, which have animals of a very similar structure, is easily understood. In Capulidee the shell is a very short cone, with a large open sub-circular mouth and an incomplete edge; it has the shell attached to the body of the animal by an adductor muscle near the hinder |
