188 CARBONIFEROUS LAMELLIBRANCHIATA. 



specimen, saw the hinge, and this proved the correctness of the original deter- 

 mination. M'Coy redescribed the species very carefully, but gave no figure. 



The original description by Phillips was very meagre, and no measurements 

 were given ; " obliquely ovate, depressed, smooth ; posterior slope ridged ; posterior 

 end truncate," comprising all that was said of it. 



De Ryckholt referred the species to Leda ; and it is very difficult to say whether 

 or no the shell should be referred to Nucula or Nuculana. The opinion of 

 observers seems to be more on the side of Nucula. This author points out that 

 the shell which De Koninck figured as his type of this species was totally different 

 from that depicted by Phillips. D'Orbigny placed together Isocardia axiniformis 

 (Schizodus) and N. luciniformis, probably confounding them as the young and 

 adult examples of one species, and referred the genus to Cardiomorpha. 



The shell appears to be fairly common in a few localities in Scotland, but I 

 have not yet seen any example from Yorkshire. 



Examples of this shell occur in all stages of growth, from the size of a pin's 

 head to that of the largest specimen here figured (PI. XIV, fig. 17), which appears 

 to be of the full size attained by the species. It is in the Woodwardian Museum, 

 Cambridge. This species is much more compressed, as a rule, than N. gibbosa, 

 the hinge-line being also straighter and comparatively longer. 



The range of this species does not appear to have been very great, as it does 

 not occur, as far as I am aware, above or below the Carboniferous Limestone series. 



Nucula oblonga, M'Coy, 1845. Plate XIV, figs. 23—27. 



Nucula oblonga, M'Coy, 1845. Synops. Carb. Toss. Ireland, p. 70, pi. xi, fig. 24. 

 Ctenodonta oblonga, Bigsby, 1875. Thesaurus Devonico-Carboniferus, p. 303. 

 Nucula oblonga, Etheridge, 1885. Brit. Foss., part 1, Palseoz., p. 287. 



Specific Characters. — Shell transversely oblong, compressed; borders sub- 

 parallel. The anterior end well developed, equal in length to about one fourth of 

 the posterior ; very slightly convex, and having an almost semicircular border. The 

 ventral border is very slightly arched, and may be straight in its middle third ; 

 posteriorly it curves upwards to join the posterior border. The latter is truncate 

 above and rounded below ; and at the extremity slightly narrower in a dorso- 

 ventral direction than the anterior part of the shell. The hinge-line is very 

 slightly arcuate, and as long as the transverse diameter of the shell. The 

 umbones are small, inconspicuous, incurved, contiguous, and situated in the 

 anterior third of the hinge-line. The valves are flattened, the dorso-ventral and 

 antero-posterior curves being very small. The greatest convexity of the shell is 

 at the umbones. There is no oblique swelling nor ridge ; no escutcheon nor lunule. 



The interior is unknown. 



