LAMELLIBRANCHIATA. . 333 



PAL^ONEILO, Hall. 1870. 



Pal^eoneilo constricta. 

 plate xlviii, figs. 1-16 ; axd plate li, fig. 17. 



Nuctditeg amstrieta, Conkad. Jour. Aead. Nat. Sci. Phila., vol. viii, p. 249. PI. 1,'), fifr. 8. 1842. 

 Niicula bellatula. Hall. Geol. Sui-v. N. Y., Rep. Fourth Dist., p. 197, t. 78, fig. 7. 1843. 

 PalcBoneilo coiistricta (Conrad), Hall. Prelim. Notice Lamellibranchiata, 2, p. 7. 1870. 



" " " " Pal. N. Y., vol. V, pt. 1. Plates and Explanations: PI. 48, figs. 



1-15. 1883. 



Shell of medium size or smaller ; ovate-cuneate, sub-nasute behind ; propor- 

 tions of length and breadth extremely variable, the length usually about 

 one-third greater than the height ; basal margin rounded in the middle and 

 anterior portions, straight or slightly constricted toward the posterior end. 

 Posterior extremity narrowed, cuneate or sub-nasute, constricted below. 

 Cardinal line abruptly declining anterior to the beak, and more gently 

 declining to the posterior. Anterior end abruptly rounded. 



Valves convex below and posteriorly, becoming gibbous above the middle 

 and in the umbonal region. 



Beaks at about the anterior third, prominent, rising above the hinge-line. 

 Umbon.al ridge rounded, not strongly defined, with a depression or undefined 

 furrow below it, which extends from just posterior to the beak to the post- 

 inferior margin. 



Surface, in well-preserved specimens, marked by fine, regular and even, 

 thread-like stria?, which frequently become obsolescent in the furrow and on 

 the post-cardinal slope. 



Anterior and posterior muscular impressions strongly marked, and with 

 umbonal muscular scars. Hinge marked by numerous crenulations, which 

 are coarser toward the anterior and posterior extremities. 



Three specimens measure respectively 20, 20 and 25 mm. in length, and 

 14, 12 and 18 mm. in height. Two extreme examples have respective lengths 

 of 23 and 16 mm. and heights of 13 and 13 mm. 



This species is of about the size of Nucula bellistriata, and striated in the same 

 manner, but is readily distinguished by its form and constricted posterior end, 

 43 



