Cochlodeftnut:] PELECYPODA. 1025 



directed resilifers, often buttressed, the lithodesma rarely wanting ; 

 ligament and area absent ; beaks fissured ; pallial sinus broad and 

 shallow 



Tertiary and Re'cent. 



Genus 1. COCHLODESMA, Couthouy, 1839. 



Cochlodesma, Couthouy, Boston Journ. Nat. Hist., ii, 1839, 170. Type : 

 Anatina Leana, Conrad. Ligula (sp.), Montagu, 1808 ; not of Block, 

 1781. Bontcea, Brown, 1844. Bortia, Gray, 1847. Galaxura, Leach, 

 1852. 



Shell inequi valve, the surface not granular, subnacreous inside, 

 slightly gaping behind and in front, somewhat inequilateral ; clavi- 

 cular rib supporting the resilifer obsolescent, and in front of the 

 resilifers there is a cartilaginous mass of dark-brown colour, uniting 

 the valves and occupying the place of the lithodesma, but uncalcified ; 

 pallial sinus oblong. 



Distribution. East coast of North America. Australasia. 

 Fossil in the Tertiary. 



1. Cochlodesma Angasi, Crosse and Fischer, 1864. Plate 61, figs. 12, a. 

 Periploma Angasi, C. & F., J. cle Conch., xii, 1864, 349 ; op. cit., 1865, 427, 

 pi. 11, f. 1. Anatina Angasi, C. & F. : Angas, P.Z.S., 1865, 644 ; Button, 

 P.L.S. N.S.W., ix, 514. Cochlodesma Angasi, C. & F. : Suter, T. N.Z.I., 

 xxxiv, 220 ; Hedley, P.L.S. N.S.W., xxvii, 17 ; Pritchard and Gatliflv 

 P.R.S. Vic., xvi (n.s.), 105 ; Index, 87 ; Hedley, T.N.Z.I., xxxviii, 72. 

 Anatina tasmanica, Reeve : Hutton, C.M.M., 61 ; J. de Conch., xxvi,. 

 44 ; M.N.Z.M., 136 ; not of Reeve. 



Shell attaining a fairly large size, inequivalve and a little inequi- 

 lateral, right valve ventricose, left valve but little convex, very thin 

 and fragile, smooth, slightly gaping at both ends, posteriorly truncated. 

 Beaks prominent, a little posterior, convex and incurved, fissuied, 

 the fissure closed up by brown conchin on the inside. Anterior side 

 slightly longer, convex, the dorsal margin horizontal and almost 

 straight, left valve with a very low oblique fold descending from the 

 beak to the anterior ventral margin ; posterior end subrostrate, ob- 

 liquely truncate, the dorsal margin a little excavated in front of the 

 beaks, straight, very little descending ; basal margin convex, ascend- 

 ing and somewhat sinuated posteriorly. Sculpture consisting of 

 irregular growth-lines, more prominent at both ends, with well-marked 

 periods of rest ; very faint microscopic radial lines. Epidermis 

 thin, light brown, forming a number of rather distant radial riblets 

 on the upper posterior end of the right valve. Colour white, dirty- 

 white where the epidermis persists. Interior white, lightly nacreou;-. 

 Margins smooth and sharp. Hinge edentulous, in each valve a spoon- 

 shaped vertical and strongly buttressed resilifer, the resilium stout, 

 extending to the margin of the valves, and uniting them. Ligament 

 wanting. Adductor-scars superficial, unequal, the anterior elongated, 

 the posterior trigonal. Pallial sinus moderately deep, rather narrow, 

 obtuse in front. 



33 Moll. N.Z. 



