180 PALEONTOLOGY OF NEW-YORK. 



Stropliodontu vaiistriata. 



Platb VIIL Fia. 1 - 16 ; and Plate XVI. Fia, 1-8. 



Strophomena varUlriata : Conrad, Jour. Acad. Nat. Sci. Philadelphia, Vol. iii, pa. 255, pi. 14, f. 6. 



S. rectilateria : Loc. citata, pa. 255, pi. 14, f. 7. 



S. imprtssa : Loc. citata, pa. 255. 



LepUtna indetda{_}] : Conrad, Ann. Rep. on the Palasontology of New- York, 1838, p. 117. 



Shjell eemioval,. varying in form from length and width equal, to length 

 greater or less than the width : hinge line equal to or greater than the 

 width of the shell below ; extremities rounded or salient. Dorsal valve 

 flat, or more or less concave according to the convexity of the ventral 

 valve, but not conforming entirely to the curvature of the latter. Ventral 

 Yalve varying from slightly convex to gibbous, and sometimes abruptly 

 arching towards the front : iimbonial region more or less prominent ; 

 beak usually a little elevated. Area narrow, almost linear. Foramen 

 linear or none*. 



Surface often finely and evenly marked with straight or slightly undu- 

 lating striae ; more often with prominent sharp striae at more or less 

 equal distances from each other, and the intermediate spaces by minute 

 equal striae ; and again in other specimens by alternating larger and 

 smaller striae, of which there are frequently three regular gradations 

 in size. Radiating striae crossed by fine concentric elevated lines, and 

 often by undulations or indentations which are more conspicuous on 

 those shells where the striae are in fascicles of finer between stronger 

 ones. Vascular impressions of the ventral valve circumscribed by la- 

 mellae, more or less distinctly flabellate : impressions of adductor 

 muscles elongate-oval. 



• The representations of the foramen on Plate viii are erroneous, there being no triangular opening of 

 the kind; this feature proving, on careful cxauiiiiation in numerous individuals, to.bc due to fracture, as is 

 common in this part of other species of the genus, and particularly io the separated valves of the typical 

 species. 



