LAMELLIBRANCHIATA OF THE LOWER MAELS. 155 



a moderate degree of arcuation, to the posterior extremity. Casts show 

 the muscular imprints to be very faintly marked but of tolerable size, and 

 the pallial sinus broad, deep, and obtusely pointed. 



I have only seen casts of this species, so that the hinge structure is not 

 known to me. Mr. Conrad mentions in his generic description of Aphro- 

 clina, of which this species is the type, that he has a single perfect left valve 

 showing the hinge characters, which lie describes as follows: "Hinge in tlie 

 left valve with three diverging cardinal teeth, the anterior tooth as thick as 

 the middle one or thicker, and a straight, compressed, transvei'sely rugose 

 lateral tooth parallel with the margin of the shell above it." I have not 

 seen the shell spoken of, and cannot judge of its merits more than is shown 

 by the figure he gives, which is copied on our plate. The species does not 

 appear to be abundant, and among the few which I have been able to refer 

 to it there is considerable variation in form, which is perhaps, to some extent, 

 due to compression and distortion in the marls. The surface of the shell, 

 so far as I can judge, appears to have been marked with fine concentric 

 lines only. Mr. Conrad's specimen, which was from Tippah County, Missis- 

 sippi, seems to have been not so high as others found in the collection of 

 the Academy of Natural Sciences labeled Merefrix Tipimna f in his handwrit- 

 ing, and the locality New Jersey. Dr. Stoliczka appears to think there was 

 little reason for separating the shell as a generic type, and considers it as 

 equivalent to Caryatis of Roemer, but has only seen the description of Mr. 

 Conrad. In its general form it diff"ers from Callista Delawarensis in being 

 more elevated, which causes a more triangular form of outline with more 

 nearly subcentral beaks. It is also of larger size as a general thing. 



Formation and locality. — In the Lower Green Marls at the deep cut of 

 the Holmdel and Keyport turnpike, Monmouth County, New Jersey, and 

 in the micaceous clays below the Lower Marl at the Rev. G. C. Schanck's 

 pits, Marlborough, and from Cream Ridge, New Jersey. One of the speci- 

 mens from the Academy of Natural Sciences collection appears to have come 

 from the first localit}^ also, the other having the appearance of coming from 

 the limestone nodules of the Lower Marls. A specimen of nearly the same 

 form, but a little doubtful, is from Freehold, New Jersey. 



