168 SYSTEMATIC ARRANGEMENT 



gills of Mr. Clark as part of the liver, and the salivary glands as the 

 gills ; and M. de Blainville has formed them into an order, under the 

 name of Cirrhobranchia. 



The animal is formed like the shell, round, and tapering gradually 

 to the posterior extremity : it is smooth, whitish, and closely in- 

 vested with a thin pellucid memhrane, beneath which two strong, 

 satiny, ligamentous muscles are seen lying along the ventral surface, 

 adhering closely, and each of them divided into a broad and narrow 

 slip. The collar is very thick and fleshy, and makes a complete 

 circle, through which the foot is pushed at pleasure. The foot forms 

 the anterior portion of the body ; it is cylindrical, thick, fleshy, 

 pointed with a conical process, and cleft above ; and in the groove 

 we see the mouth in the shape of a compressed process, projecting 

 forwards, and with its edge friDged with short tentacular papillae. — 

 Johnston, Trans. Berw. Nat. Club, ii. 39. 



They live buried in the sand or sandy mud in from ten to one 

 hundred fathoms. The gills are pale green. The hinder termina- 

 tion of the shell, when perfect, is tapering, with a short notch on 

 the dorsal or arched side of the shell ; or if it is truncated, then it is 

 furnished with a lateral, tubular projection, rather broadly fissured 

 on the dorsal edges. 



1. Dentalium. 

 Shell tubular, tapering, curved; apex truncated, with a simple 

 perforation ; aperture circular. 



1 . D. ? semistriolatum, Linn. Trans, t. 1 15. f. 4 ; Chiaje, t. 1 15. f. 3. 



When the apex of the shell is broken off, it is reproduced by a spur- 

 like process on the edge. 



2. Entalis. 



Shell conical, elongate ; apex truncated, with a longitudinal 

 fissure on the dorsal or hinder margin ; mouth circular. 



1. E. vulgaris, t. 115. f. 2, t. 116. 



Central tooth of Entalis vulgaris subsemicircular, oblique, flat ; 



Fig. 90. — Teeth of Entalis vulgaris. 



base somewhat straight ; margin waving ; cutting edge unarmed ; 

 lateral tooth with a compressed angular scape ; hook with an inflexed, 

 blunt angle ; apical margin denticulated in front ; limb with a large, 

 bent, rhomboidal lamina, elongated (fig. 90). 



The young have the apex of the shell slightly inflated, with a 

 rather oblique oval aperture. The shell of the younger specimens 

 is more arched near the top ; the older specimens become trun- 



