732 DR. J. E. GRAY ON THE CALYPTR^ID^. [Juiie 27, 



smaller groups, and according to the structure of the raollusca 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 ex- 

 tended 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 " On 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 ex- 

 pensive 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 differ- 

 ence between the two families CalyptrceidcE and CapulidcB, which 

 have animals of a very similar structure, is easily understood. 



In CapuUdcti the shell is a very short cone, with a large oj)en sub- 

 circular mouth and au incomplete edge ; it has the shell attached 

 to the body of the animal by an adductor muscle near the hinder 



