CHARACTERISTIC DEEP-SEA TYPES. GASTEROPODS. 71 



Another illustration of the fragile and delicate forms living 

 in the abysses is Triforis longissimus (Fig. 295), only thir- 



Fi. 295. Triforis longissimus. f. 



teen hundredths of an inch in diameter, with a column of 

 twenty or thirty whorls, reaching an inch to an inch and a 

 half in length ; the perfect shell must have over forty turns, 

 but it is always decapitated. Siliquaria modesta (Fig. 296), 



Fig. 296. Siliquaria 

 modesta. I- 5 . 



Fig. 297. Vermetus 

 erectus. -* 6 . 



one of the irregular gasteropods, with a slit like a Pleurotoma- 

 ria, so frail as almost to perish with a touch, lives in the -soft 

 mud of the abysses, while the stouter Vermetus erectus (Fig. 

 297) finds a foothold on dead corals and shells. The species 

 of this genus are comparatively shallow- water animals. 



The majority of the bivalves are characterized by great deli- 

 cacy of shell and sculpture. In the deep-water representatives 

 of the family of scallops, the constituent prisms are often large 

 enough to be seen with the naked eye, and the shell is strength- 

 ened within by slight riblets radiating from the hinge. Pecten 



