471 



NUCULA. 



port Narrows, Perry Co., Pa. Specimen 77 d^ 13, in Hamilton 

 upper shales, VIII c. 



Nucula shumardana. 



tndJ^n. 



A.P.S. 



Hall, Trans. Alb. Inst. 1856. Also 



Collett's In^ 



diana E t. 



1882, p. 343, 



/ plate 30, figs. 



"-^^ "r, JO, 2, 3, enlarged 



twice, usual form; figs. 4, 5, longer than usual; f. 6, enlarged 

 three times, outline showing hinge. Sub carloniferous lime- 

 stone, at Spergen Hill, etc., Ind. — XI 



Nucula sinuosa. Simpson, new species, 1888. Shell 



small, ovate cuneate in outline, subna- 

 sute behind; height varying from one- 

 half to two-thirds the length, usually 

 slightly more than one-half ; anterior and 

 middle portions of the basal margins 

 rounded, somewhat abruptly constricted 

 towards the posterior end ; posterior 

 Tr. 1889 margin obliquely truncate ; anterior end 

 abruptly rounded ; cardinal line, anterior to the beak, sharply 

 declining; more gradually sloping to the posterior. Valves 

 slightly convex, greatest thickness of the shell a short distance 

 below the umbo. Beaks from one-third to three-fifths of the 

 length of the shell from the anterior end, extending above the 

 hinge line, compressed, sharp, not prominent. Umbonal ridge 

 distinctly defined, subangular, with a shallow depression below 

 it, which is most conspicuous at the postbasal margin, becom- 

 ing obsolete on the upper half of the shell ; posterior slope 

 marked by fine, sharp, slightly divergent striae. There are 

 also fine concentric striations, which on the specimens observed 

 are obscure, the surface appearing smooth. Hinge line marked 

 by frequent crenulations. Three specimens measured have 

 each a length of 10 mm. ; height varying from 5 to 7 mm. In 

 the striation of the posterior slope this species resembles 

 Nucula poststriata, of the Trenton and Hudson river groups, but 

 may be distinguished from that species by its less gibbous form, 

 the constriction of the postbasal margin, and the conspicuous 

 depression below the umbonal ridge. Formation and locality, 

 3 



