170 AMERICAN MARINE CONCHOLOGY. 
Genus CRYPTODON, Turton. 
Brit. Bivalves, 121. 1822. 
1. C. Gounpr, Philippi. Fig. 430. 
(Lucina.) Zeit., Malak., 74. 1845. 
Lucina flexuosa, Gould (not Montagu), Invert. Mass., edit. i. 71, f. 52. 
Shell minute, white, ovate-globose, nearly equilateral; beaks 
prominent, inclined forwards, and having a rounded impression in 
front of them; surface smooth, white; glossy within, with minute 
radiating lines. 
Length 7.5, height 8 mill. 
New England. 
2. C. opEsus, Verrill. Fig. 431. 
Am. Journ. Science, 287, t. 7, f. 2. 1872. 
Shell white, irregularly and rather coarsely concentrically 
striated, much swollen in the middle; transverse diameter nearly 
equal to the length; height considerably exceeding the length; 
beaks prolonged and turned strongly to the anterior side; lunular 
area rather large and sunken, somewhat flat, in some cases sepa- 
rated by a slight ridge into an inner and an outer portion; anterior 
border with a prominent rounded angle; ventral margin prolonged 
and rounded in the middle; posterior side with two strongly 
developed flexures, separated by deep grooves: interior of shell 
with radiating grooves, most conspicuous toward the ventral edge. 
Length 15, height 18 mill. 
British America. 
More nearly related to C. flexuosus of Europethan to C. Gouldii. 
The latter is thinner and more delicate, more rounded, relatively 
much longer and much smaller. 
Genus MYSIA, Leach. 
Menke, Syn., edit. ii. 112. 1830. 
1. M. punoTaTA, Say. 
(?Amphidesma.) Journ. Philad. Acad., ii. 308. 1822. 
Orbicular, with numerous minute concentric wrinkles and very 
numerous minute punctures; within, a small rim or projecting line 
runs near the edge from the hinge to the basal margin. White. 
Length and height 7.5 mill. 
Southern Coast. 
