47 



concentric lines under a magnifier. Length and width about 4 lines. 

 Six miles east of Otter River, near Jupiter River and the Jumpers ; Divs. 

 2, 3, 4. J. Richardson. 



This species is somewhat similar in form to A. congesta, Conrad, 

 which abounds in the Clinton formation in New York, but differs there- 

 from in having the mesial fold and sinus shorter. 



A. TUMIDULA, n. sp. — Sub-orbicular ; -width sHghtly greater than the 

 length ; apical angle about 105* ; sides nearly straight for a little over 

 one third the length from the umbo, rounded in the middle third and to- 

 wards the front margin ; the latter with a broadly convex lobe. Ventral 

 valve rather strongly convex, nearly uniformly arched from beak to front, 

 the most abrupt curve being above the middle ; umbo moderate ; beak 

 small, incurved down to the umbo of the opposite valve ; front margin 

 produced into a curved rounded Imguiform lobe from each side of which a 

 faint, barely perceptible depression runs towards the beak, the space be- 

 tween them with about the average convexity of the valve. Dorsal valve 

 less convex than the ventral, sub-carinate along the middle, sloping to the 

 sides ; mesial fold at the front nearly one-third the whole width, strongly 

 elevated, rounded along the crest, becoming obscure or so little developed 

 above the mid-length as to produce only an obtuse median carination ; on 

 each side of the fold a faint rounded sinus outside of which the shell has a 

 somewhat flat slope to the sides ; umbo moderate , beak curved beneath 

 that of the opposite valve. The hinge line of this valve is nearly straight 

 for more than half the whole width. When the shell is a httle exfoHated 

 there can be seen on each side of the umbo two dark Unes radiating from 

 the beak indicating a pair of short septa. Surface smooth. Length of 

 large specimen 9 lines ; width 10 lines. Near Jupiter River and four 

 miles west of South-west Point ; Div. 3, A. G. J. Richardson. 



This species resembles A. tumida, Dalman, but is smaller, more angu- 

 lar along the middle, the hinge line of the dorsal valve straighter, and has 

 two short septa radiating from the beak instead of one. 



A. LAKA, n. sp. — Shell lenticular, sub-pentagonal or sub-ovate, great- 

 est width a httle above the middle where it is equal to or a httle more or 

 less than the length ; apical angle usually about 120'^ ; sides straight or 

 gently concave from the beak to the cardinal angles, rounded in the mid- 

 dle third ; somewhat straight and converging in the lower half ; the front 

 margin straight or gently convex in the middle. Both valves are mode- 

 rately and about equally convex ; umbo and beak of ventral valve small, 

 the latter closely incurved ; umbo of dorsal valve distinct but not promi- 

 nent, beak buried ; hinge-line in most specimens straightish. Surface 

 smooth. Length and breadth 6 or 7 hues ; depth of both valves 4 lines. 

 Gull Cape ; Div. 2, A. G. J. Richardson. 



