CARBONIFEROUS FOSSILS OF IRELAND. 69 



equilateral triangle ; posterior side one-half longer, tapering, rounded at the point ; margin sinuous ; surface 

 finely striated transversely, with a few deeper lines of growth. 



This curious little shell is not unlike that of a Teredo ; it is exceedingly rare, only one specimen having 

 as yet occurred. Length two lines, width three and a half lines. 



NUCULA CLAVATA. M'Coy. (PI. XL fig. 25). 



Sp. Ch. — Transversely ovate, gibbous; twice as wide as long; anterior side obtusely rounded ; posterior 

 end produced one-third longer than the anterior; subtruncate, obtusely rounded; an obtuse ridge extends from 

 the beak to the jjosterior-inferior angle ; surface marked with somewhat irregular, transverse strise, and broad, 

 fiat, intermediate spaces ; a few of the striaj deeper than the rest, particularly near the margin. 



This species is easily distinguishable from the Nucula attenuata, Flem., and N. acuta, Sow., by the very 

 obtusely rounded posterior end : in general appearance it comes nearest to the N. claviformis. Sow. {N. ros- 

 tralis. Lam.), but that is a Lias species, and has a much narrower posterior ridge, and the extremity is abruptly 

 truncated ; the striaj arc of a peculiar form in the present shell, appearing as if imbricated with the fine edge 

 towards the beak. Length four lines, width eiffht lines. 



& 



Nucula CYLiNDRicA. M'Coy. (PI. XL fig. 26). 



Sp. Ch. — Transversely elongate, twice as wide as long, very convex, cylindrical, rounded at both e.xtrcmi- 

 ties ; beaks very small, close to the anterior end ; dorsal and ventral margins slightly convex ; two long, curved, 

 diverging, subrostral plates ; surface smooth, or with traces of oblique striaj towards the margin. 



This is one of those very interesting species in whicli there are well developed Internal plates beneath the 

 beak; the external form is allied to that of the Lithodomi. Length three lines, width six lines. 



Nucula DELTA. M'Coy. (PI. XI fig. 22). 



Sp. Ch. — Trigonal, compressed; anterior side abruptly truncated; posterior end obtusely pointed; dorsal 

 and ventral margins slightly convex ; surface smooth, with a few transverse wrinkles of growth. 



The triangular, flattened form of this Nucula distinguishes It easily from every other Palasozoic species ; the 

 surface seems to have been smooth, or with one or two faint, distant waves of growth. Length five and a half 

 lines, width six and a half lines. 



Nucula gibbosa. Flem. 



Nucula gibbosa. Flem. Brit. Anim. — Nucula tumida. Phil. Geol. York. 



Sp. Ch. — Transversely ovate, gibbous; beaks large, tumid; length two-thirds the width, depth of the two 

 valves equal to the length ; surface smooth, with few concentric strise. 



This species has been described under the name of N. gibbosa by Dr. Fleming, from the Glasgow coal 

 field, where it is very common. Professor Phillips subsequently described it under the name of N. tumida, 

 without allusion to Fleming, whence I conclude that author's description must have escaped notice ; I have, 

 therefore, restored the original name above. This greatly resembles the recent N. margaritacea of our coasts. 

 Length four lines, widtli seven fines. 



Nucula leiorynchus. M'Coy. (PL XL fig. 27)- 



Sp. Ch. — Transversely ovate, width rather more than twice the length, convex; posterior end rounded, 

 gibbous ; anterior end produced into a long, narrow beak, rounded at the point ; surface marked with strong, 

 regular, equal, transverse strise, which disappear as they reach the anterior end, leaving the long, beak-Hke, ante- 

 rior extremltv smooth. 



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