CHARACTERISTIC DEEP-SEA TYPES. CASTEROPODS. 



69 



Fig. 287. — Leptothyra 



iiiduta. |. 



the case of the former to the application of several specific names. 



The depth in which these have been found 



varies from 125 to over 1,000 fathoms. 



Pleurotomaria is one of the most remark- 

 able forms dredged in the continental region. 



Four recent species of the genus are known. 



Its history dates back to the earliest fossilifer- 



ous rocks of the cambrian, and to the dreds"- 



ings of the "Hassler" and the " Blake" are 



due the only knowledge yet acquired of its 



soft parts. Two species are found in the 



West Indies, of which the 

 finest is P. Adcmsonlana 

 (Fig. 288), from about 200 

 fathoms. The shell is four 

 inches in diameter, richly 

 pearly within, and orna- 

 mented with elegant red 

 and brown colors exter- 

 nally. The anal notch in 

 this species extends nearly 

 half the length of the last 

 whorl. A second species, 

 less brilliant and with a 

 shorter notch, is P. Quoy- 



Fig. 288. — Pleurotomaria Adansoniana. *. /t-,. nc^fw ^ i 



ana (rig. lo\)), also ob- 

 tained living by the " Blake." 



Among other univalves, the Mar- 

 ginellidae are represented by such 

 species as Marglnella succinea Con- 

 rad, extending from shallow water 

 • to several hundred fathoms, and M. 

 Watsoni (Fig. 290), characteristic of 

 great depths. The Ringiculidae, of 

 which many species are known fossil, 



are illustrated by R. leptOche/da Fig. 289. — Pleurotomaria Quoy- 



(Fig. 291), described first by Brug- ''^"^- '• 



none from the Mediterranean, and afterward from deep water 



