138 COCCULINA-ADDISONIA. 



oval muscular impressions, and the prominent head-scar shaped like 

 that in Patella, only somewhat larger in proportion. (Watson.*) 

 Length 0'13, breadth 0'07, height 0'07 in. 



Philippines, 20 fms. 



Cocculina angulata WATS. Challenger Rep. Gastrop., p. 30, t. 4 r 

 f. 2. 



This species belongs to Dr. Dall's section Coccopygia. 

 Family ADDISONIID.E Dall, 1882. 



Shell asymmetrical, porcellanous, something like Caplulacmcea, 

 Sars. 



Soft -parts much as in the last family, but strongly asymmetrical, 

 with an enormously developed lateral series of separately inserted 

 gill-laminse, like those of Patellidce, and without filamentary append- 

 ages of any kind. Radula with a large simple rhachidian tooth 

 with, on each side, two large, simple transverse laterals, followed by 

 two minute ones, and a large outer lateral with a strong tridentate 

 cusp, outside of which is a single scale-like flat uncinus, bearing an 

 elongated thickened ridge, but no cusp. 



This family might be incorporated with the last were it not for 

 the differences in the branchiae and in its dentition. These latter are 

 of great weight. The dentition of Addisonia is like nothing known 

 in the whole group of Rhiphidoglossa, but, while it recalls the den- 

 tition of the Chitonidse in some features, has a decidedly docoglossate 

 aspect. Perhaps the most rational hypothesis is that this group 

 bears to the preceding family much such a relation as in Pulmo- 

 nata is borne by Cyclotacea of Troschel toward the Cyclostomacea, 

 indeed, the resemblance of the radula of Cocculina rathbuni to that 

 of the species of Helicina figured by Troschel is quite remarkable. 

 This family contains, so far as known, but one genus. (Dall.) 



Genus ADDISONIA Dall, 1882. 



Addisonia DALL, Proc. U. S. Nat. Mus. 1881, p. 405, April 1882 ; 

 Rep. on Blake Gastrop., p. 344. JEFFREYS, P. Z. S. 1882, p. 673 ; 

 1884, p. 148. FISCHER, Manuel, p. 757. WATSON, Challenger 

 Rep. p. 32. 



Shell ovate, subconical, strongly symmetrical, porcellanous, thin ; 

 with a blunt apex curved backward, downward, and to the left, 

 without an epidermis ; with an unthickened, simple, entire margin ; 

 pedal muscular impression horseshoe-shaped, interrupted in front. 



