CARBONIFEROUS FOSSILS OF IRELAND. 57 



At first I imagined this to be only a monstrous variety of tlie Cardiomorpha oblonga, but I have since seen 

 other specimens, perfectly similar, and I am assured they are not luicommon In the Cork limestone. It is 

 much more gibbous than that species, and most so In young individuals, the margin being abruptly deflected 

 in specimens of one inch in width, so that in large specimens the marks of growth are very prominent, that 

 nearest the beak being raised nearly half an inch above the surface; nearer the margin, the second mark is 

 less prominent, the third still less, and so to the edge ; the surface is quite smooth, except towards the margin, 

 where it is striated concentrically. Length one inch ; width one inch five lines ; depth one inch six lines. 



Pleurorynchus. Phil. 



Gen. Ch. — Shell fusiform ; posterior side produced, rounded, gaping ; anterior side truncated, often pro- 

 tected by an extension of the shell at the keel which bovmds it, produced near the beaks into a long, slender tube. 



No generic characters having been originally given for the genus Pleuronjnchu.i, must surely have been 

 the reason why this excellent genus has not been more generally adopted. As both Goldfuss and Mr. Sowerby 

 continue to place these shells in the genus Cardium, I may be pardoned for furnishing generic characters of my 

 own, and also a few details as to the structui'e of the perfect shells, which, I believe, have not come under the 

 notice of preceding writers. All the species of Pleurorynchus are more or less fusiform shells, subtruncate at the 

 anterior end ; the body of the shell is large and gibbous ; the posterior side is rather suddenly attenuated, rounded 

 at the end, and gaping widely, resembling, in fact, the corresponding part of a Pholas dactylus; the antenor 

 side is truncated, bordered by a shelly margin, varying in depth according to the species ; near the beak, a long 

 slender tube extends to a length often exceeding the length of the shell. The substance of these curious shells 

 is exceedingly thick, finely striated on the outside, but strengthened internally by strong, radiating ribs, and 

 presenting internally a cellular structure. The wide gaping of the posterior end shews, that like the Mya 

 truncata, or the Pholas alluded to, it must have lived habitually buried in the sand, with its long siphons 

 reaching to the surface. The resemblance to Cardium (or rather Hemicardium), seems to be one merely of 

 general resemblance, and entirely at variance with the true structure of the genus, as seen in the figure of P. 

 fifsiformis, M'Coy. Professor Agassiz' reference of the genus to the Brachiopoda Is, I confess, quite unintelli- 

 gible, the Brachiopoda being essentially equilateral, from their structure, and the Pleurorynchi remarkably in- 

 equilateral; neither does its reference to the Rudistes, from the microscopic structure of the shell, seem more 

 tenable, the structure alluded to being present in several other shells. Its true station seems to be between 

 Mya and Pholas. 



Pleurorynchus alieormis. Sow. sp. 



Cardium aliforme. Sow. Min. Con. and Geol. Tr.— Pleurorynchus aliformis. Phil. Geol. York.— Cardium aliforme. 



Gold. Pet. 

 Sp. C/^— Heart-shaped, gibbous; anterior side convex from the keel, which borders it, gradually rising to 

 form the conical, anterior tube ; posterior side rather short, conoid ; surface, with radiating nbs, nearly equal on 

 all parts of the shell. 



This species is readily known from the P. minax, by Its anterior side rising at once Into a conical umbo, 

 not exhibiting the central concave space of that species ; the radiating ribs also are of nearly the same size on 

 the anterior end as on the body of the shell in this species, in which it also differs from the P. mmax. This 

 species is very rare in the carboniferous limestone, where the other is abundant, this being, on the other hand, 

 common In the Inferior slates. Length five lines, width ten lines. 



Pleurorynchus armatus. Phil. 



Pleurorynchus armatus. Phil. Geol. York. 

 Sp. CA.— Aliform, anteriorly subtruncate, produced Into a slender tube, equalling or exceeding the pos- 

 terior side in length; posterior side one-third longer than the length of the shell, compressed; surface re- 

 gularly striated from the beaks. 



