GASTEROPODA. 187 



and on the lateral areas the striae are transverse or diverging ; apophyses subangular, 

 projecting, and sublateral. 



Altitude of arch, ^ the span. 



Locality. Cor. Crag, Sutton. ? Mediterranean. 



Single valves of this species are abundant. It was considered in my Catalogue as 

 a distinct species ; I have now united it with the above Mediterranean species, from 

 its general resemblance, although with considerable doubt. The lateral areas have 

 the granules in transverse or radiating striae, not quite so regular and distinct as those 

 upon the dorsal area ; but the primal as well as the final valves have the different areas 

 striated in a radiating manner. The projecting processes are near the sides, and are 

 of an obtusely-angular form, somewhat resembling the blade of a lancet used for 

 bleeding cattle. On the final valve they do not project so much, and extend further 

 along the margin inwards. Fig. 1 1 a is the primal valve ; 1 1 6, one of the central 

 valves ; 1 1 c, the terminal or final valve. 



There is every reason to believe that two more species of the genus Chiton existed 

 during the Coralline Crag period, valves of which are in my cabinet. They are not, 

 however, in sufficiently good preservation for description, and their characters cannot 

 be accurately determined. 



ORD. CIRRIBRANCHIATA. 

 DENTALTUM.* Linn. 1740. 



TUBULUS Scilla. (ex Hermansen.) 

 SOLEN (spec.) Rumph. Id. 



Gen. Char. Shell tubular, symmetrical, elongate- conical, or subcylindrical, generally 

 smooth, sometimes annulated, often costated, slightly curved, open at both ends, 

 smaller at the posterior extremity, which is sometimes entire, sometimes with a medial 

 and dorsal cleft, occasionally with two lateral indentations. 



Animals of this genus are now determined to be true Mollusca, though belonging to 

 a distinct order, having the branchiae near the upper part of the neck, in the form of 

 two bundles of fine, soft, flexible, tentacular filaments. They are placed in a natural 

 arrangement near the Patellae. M. Deshayes, in a Memoir read before the Societe 

 d'Hist. Naturelle, 1825, gave the anatomical details of one species, and a monograph 

 of the genus. In his description he places the shell with its small end downwards, 

 considering it the posterior extremity ; and the convex portion of the shell, as cor- 

 responding with the dorsal surface of the animal ; the larger end, therefore, is the 

 anterior. 



* Etym. Dentale, from dens, a tooth. 



