1890.] NATL'RAL SCIENCES OF PHILADELPHIA. 159 



crinoids the station of each individual is definitely known. As stated 

 already, the firstofthese formsgenerally rests on flat-vaulted crinoids ; 

 while the second connnonly adheres laterally to such echinoderms as 

 Platycrinns hem isphericus. Cajmlus eqmlatercd'is when occupying the 

 same position is pendant, the apex of the shell being directed down- 

 ward instead of in the opposite direction as when resting on the 

 ventral surface of such species as Gilbertsocrimis. The shell thus 

 pendant exhibits a decided tendency to straighten, or uncoil, con- 

 sequently becoming longer, the apex freeing itself completely from 

 the body whorl. In comparison, therefore, with a representative 

 example of C. equilateralis those shells resting on flat eriuoidal vaults 

 are very much depressed, the aperture proportionally broader and 

 the spire more closely coiled. Those individuals attached laterally 

 to crinoids have a tendency to become more conical, the aperture 

 being relatively smaller, while the spire is entirely free from the last 

 volution and the apex often extends to a considerable distance be- 

 yond the posterior margin of the aperture. 



On the other hand Capulus infundihulum is commonly a mure or 

 less elongate conic shell. AVhen attached to Platycrinus it often 

 assumes a very different aspect. As growth proceeds the posterior 

 side becomes relatively shorter, the apex slightly curved backwards 

 and not unfrequently there is a marked tendency toward a strongly 

 arcuate form. 



II. Geographic and Geologhc Distribution. 



General Considerations. The Calyptrteidre are widely distributed 

 both in space and time. The earliest appearance of this group of 

 gasteropoda is in the Calciferous strata of the Lower Silurian. From 

 this time onward its development is rather rajDid, and attains a 

 considerable expansion in the upper paleozoic, where in numerical 

 representation, size and variety of form it is rather remarkable. 

 There is then a gradual and general decline toward the close of the 

 paleozoic. The ancient Capuli are confined chiefly to Europe and 

 North America, though two forms have been described from the 

 Carbonic rocks of Australia. During Silurian and Devonian times 

 New York seems to have been the great center of the development 

 of this group ; while in the interior of the American continent these 

 gasteropods did not become common until the beginning of the Car- 

 bonic. 



Range of American Species. Relative to the geographic and 

 geologic distribution of the American species of Capulus during 



