396 BRITISH PALALOZOIC FOSSILS. [ LAMELLIBRANCHIATA. 
I have only seen the trace of the lateral hinge-tooth in two specimens; it is very delicate, and declines 
only slightly from the hinge-line, of which it runs the greatest part of the length; some very small specimens 
are as acutely and obliquely ovate as the large ones, but they are probably old dwarf specimens; others of 
larger size, which are less oblique and less acute at the posterior end, and which I imagine to be the young, 
have their outline exactly paralleled by the lines of growth near the beak of the large acutely ovate specimens. 
Position and Locality—Extremely abundant in the decomposing sandstone of Marwood Quarry, near 
Barnstaple. 
Genus. ANODONTOPSIS. See page 270. 
ANODONTOPSIS DELTOIDEUS (Phill. Sp.) 
Ref. and Syn.= Cypricardia deltoidea Phill. Pal. Foss. f. 59. . 
Sp. Ch.—Ovato-rhomboidal, compressed, smooth ; anterior side and ventral margin semicircularly arched 
from the beaks as far as the middle of the length, the remainder of the ventral margin forming a tangent ; 
posterior end obliquely subtruncate, the margin gently convex, inclined at about 75° to the ventral margin, the 
respiratory angle being narrow, rounded; angle between the hinge-line and posterior margin about 125° ; 
greatest depth of the valves along a strongly marked, angular, diagonal ridge, distinct from the beak, to the 
respiratory angle; posterior slope and sides of the valves flattened, the latter slightly convex ; hinge-line short, 
straight, slender, lateral tooth or cardinal teeth extending nearly its length, and close below it. Length from 
anterior end to respiratory angle of large specimen one inch three lines, proportional width from beak to ventral 
margin at right angles to the hinge 7, length of hinge-line ;;,, width of posterior margin = to 4, length of 
anterior end 34, greatest depth of both valves in young, ,{, in old specimens. 
Position and Locality—Not uncommon in the sandstone of Marwood, and in the prolongation of the 
same beds at Baggy Point. 
Genus. LEPTODOMUS. See page 277. 
Lrertopomus constrictus (M‘Coy). Pl. 2. A. f. 10*. 
Sp. Ch.—Oblong, or subtrigonal from the projection of the very prominent beaks; valves very tumid 
towards the anterior side, greatest depth at about one-third from the beak; anterior end subtruncate, pro- 
jecting but slightly towards the ventral portion beyond the line of the beaks ; anterior lunette very large, ovate, 
deep, smooth; a deep narrow sulcus extends from the beak, slightly widening to the nearly straight ventral 
margin, which it meets at little more (95°) than right angles, forming a small sinus ; posterior side much com- 
pressed; posterior slope not defined; posterior end obtusely subtruncate, with a slight obliquity ; hinge-line 
straight, rather shorter than the posterior side; anterior side and middle of the valves deeply marked with 
coarse concentric wrinkles, arising from the edge of the smooth anterior lunette, and most of them becoming 
abruptly obsolete on the posterior half of the shell, those near the margin of old specimens about one line 
wide, gradually diminishing towards the beak. Length one inch two lines, proportional width from beak to 
opposite ventral margin 4, length of anterior lunette =, width of posterior end about jj, depth of right 
valve ;%. 
This species in size, shape, subtruncate anterior end, and coarse concentiic wrinkles of the anterior half, 
becoming obsolete on the posterior portion, almost exactly resembles the LZ. truncatus (M*Coy) of the Upper 
Ludlow rock, but may be distinguished easily by the strong divisional sulcus from the beak. I suspect the 
fossil from Baggy Point, referred by Phillips (Pal. Foss.) to the Silurian so-called Cypricardia impressa of 
Sowerby, may be found to belong rather to the present species. 
Position and Locality.—One young specimen five lines long of the left valve, and two large specimens in 
apposition of the right valve, have occurred in the sandstone of Marwood, North Devon. 
Explanation of Figure.—Pl. 2. A. fig. 10*, natural size, right valve. 
