Glycymeris.] PELECYPODA. 851 



ligament external, its area distinct and with diverging grooves ; car- 

 dinal border regularly arched or semicircular ; teeth prominent, 

 strong, short, numerous, becoming obliterated under the umbones as 

 the gerontic stage is approached, by the invasion of the ligamental 

 area ; margins of the valves crenulated ; adductor-scars subequal ; 

 pallial line simple. 



Distribution. About sixty species are known from Australasia, 

 west coast of America, Indian Ocean, Antilles, seas of Europe, &c., 

 living in sandy gravel from about 5 to 90 fathoms. 



Fossil. Cretaceous and Tertiary. 



Vernacular Name. Dog-cockle or comb-shell. 



KEY TO SPECIES. 



A. Shell attaining a large size, with broad rounded radiating ribs . . laticostata. 



B. Shell small, finely radiately striate . . . . . . . . modeskt. 



1. Glycymeris laticostata, Quoy and Gaimard, 1835. Plate 56, 

 figs. 3, 3. 



Pectunculus laticostatus, Q. & G., Voy. Astrol., iii, 1835, 466, pi. 77, f. 4-6 ; 

 Conch. Icon., i. 1843, f. 8 ; Dieff. N.Z., 257 ; C.M.M., 80 ; Crit. List, 49 ; 

 Hutton, J. de Conch., 1878, 53 ; M.N.Z.M., 163 ; P.L.S. N.S.W., ix, 

 528 ; C. Tert. M.B.M., 341. P. ovatus, Q. & G., I.e., 467, pi. 77, f. 1-3. 

 P. Maccoyi, .Johnston, P.R.S. Tas., 1884, 199. Glycymeris laticostata, 

 Q. & G., Index, 94. 



Shell attaining a large size, thick and solid, orbicular, convex, 

 equilateral or subequilateral, with broad rounded radiating ribs. Beaks 

 median, distant, turned inwards and very slightly forwards, pointed. 

 Anterior and posterior end broadly convex, with straight dorsal mar- 

 gins ; the basal margin regularly arched. The ligamental area long, 

 narrowly elliptical. Sculpture consisting of broad rounded radiating 

 ribs, obsolete towards the margin in old individuals, crossed by tine 

 concentric lines and well-marked growth-periods towards the margins. 

 Epidermis lost in all specimens I have seen. Colour reddish or 

 yellowish-brown, often variegated with white. Interior white or 

 brownish, finely radially striated, porcellanous. Margins crenated in- 

 side on the lower half of the valves. Hinge-plate arcuate, moderately 

 broad in the middle, but widening on both ends ; young shells with a 

 few small oblique teeth under the beaks, and about 6 oblique or nearly 

 horizontal teeth on each side ; in adult shells the ligamental area is 

 getting very high, the hinge-plate very narrow in the middle, and 

 the teeth on each side are reduced in number to 2 or 3. Ligament 

 in divaricating external grooves. Adductor-scars distinct, subequal. 

 Pallial line simple. 



Length, 70 mm. ; height, 73 mm. ; diameter, 50 mm. Length, 

 105mm.; height, 110mm.; diameter, 60mm. (large form). 



Type in the Mus. Hist. Nat., Paris. 



Hab. Throughout New Zealand. Cape Maria van Diemen ; Bay 

 of Islands ; near Cuvier Island, in 38 fathoms ; Hauraki Gulf, from 



