70 SYNOPSIS OF THE CHARACTERS OF THE 



This elegant little species resembles the N. acuta, Sow. (not of Portk.), and N. attenuata, Flem. {N. cla- 

 viformis of Pliil.) in general form and striation, but differs in the smoothness of the rounded anterior rostrum ; 

 it is also analogous to the N. rostralis, Lamk. (N. claviformis. Sow.) of the Lias, but it is distinguished, besides 

 their o-eological localities, by tlie present shell having the anterior extremity pointed, as well as smooth, while 

 it is distinctly truncated in the former shell. Length one line and a half, width four lines. 



NUCULA LINEARIS. 

 Nucula lineata. Phil. Pal. Fos. 



Sp. C/i.— Transversely trigonal, convex; anterior side subtruncate, rounded; posterior end produced, 

 pointed, extremity rounded ; surface regularly marked with strong, concentric stris ; between each pair are 

 three or four finer lines. 



This small species is very rare ; the two varieties are met with, the one with the larger strias crenulated, 

 and the other with all the stria plain ; both states of surface are occasionally found on the one specimen. The 

 name lineata having being previously used for another species by Mr. Sowerby, I have modified it as above. 

 Length four lines, width five lines. 



Nucula longirostris. M'Coy. (PI. XL fig. 19)- 



Sp_ C/(.— Transversely clavate; width two and a half times the length; anterior side produced into a very 

 long, narrow beak, abruptly truncated at the end ; posterior side moderate, rounded ; surface very finely striated 

 transversely. 



Tliis beautiful little shell is easily distinguished from the N. acuta, and other claviform species of the Palre- 

 ozoic period, by its distinctly truncated anterior extremity, in which it approaches the N. claviformis, Sow., 

 N. rostralis. Lam.), this latter shell, however, belongs to a different formation, and is, besides, distinguished by 

 its coarse stria, and is less elongated transversely. Length two lines and a half, width five lines and a half 



Nucula OBLONGA. M'Coy. (PL XL fig. 24). 



Sp.Ch. — -Transversely oblong ; width twice and a half the length, convex; dorsal and ventral margins 

 parallel, straight ; beaks inconspicuous, close to the anterior end ; anterior end small, rounded ; posterior end 

 subtruncate, abruptly rounded ; surface smooth. 



This shell is distinguished by its great transverse diameter, subtruncate, posterior end, and the parallelism 

 of the hinge-line and abdominal margin ; the posterior end being as wide as any other part of the shell. 

 There are traces of a subrostral plate, as in the N. cylindrica, M'Coy, and N. solenoides, Goldf Length three 

 lines, width eight lines. 



Nucula Phillipsii. 



Nucula undulata. Phil. Geol. York. 



Sp. Ch. — Transversely ovate, depressed, width nearly twice the length; beaks small, subcentral; anterior 

 end rounded ; posterior end narrowed, compressed, subtruncate, rounded, defined only by an obtuse ridge from 

 the beak ; surface concentrically striated. 



This is a large, depressed species, chiefly remarkable for the obtuse diagonal ridge, which runs from the 

 beak to the front posterior angle, and its blunt, subtruncated, posterior end ; the beaks are more nearly central 

 than is usual in this genus. As there is already a Nucula undulata in the superior strata, I venture to make 

 the above alteration in the specific name. Length six lines, width eleven lines. 



