58 SYNOPSIS OF THE CHARACTERS OF THE 



This species is very closely allied to the young of P. aliformis, but is apparently distinguished by the great 

 length of the anterior tube. 



Pleurorynchus fusiformis. MCoy. (PI. IX. fig. 3). 



Sp. Ch. — Transversely fusiform; posterior extremity narrow gaping; anterior extremity gibbous; the 

 margin much prolonged, pointed vontrally, with an inflexed edge, forming a very deep, anterior chamber 

 round the truncated, anterior face, from which the slender, conical tube rises abruptly ; surface finely striated 

 concentrically ; lips rugose ; internal longitudinal ribs large, -strong, and sharp. 



This splendid species vies with the Pleurorynchus giganteus, M'Coy, in size ; it is distinguished from 

 it, and, indeed, all others, by its fusiform contour, produced by the contraction of the anterior margin, the 

 edge of which is suddenly inflexed to about Iialf an inch in width ; the substance of the shell is amazingly 

 thick, half an inch being the usual thickness of adult specimens ; the sui'face is concentrically striated from the 

 beak ; these strise become very large and rugose near the edge, owing to the thickening of the lips in old spe- 

 cimens ; internally the surface is strengthened by large ribs from the beak ; the posterior half of the shell is 

 narrow, compressed, round at the end, and gapes very considerably. Length three inches and a half, width 

 from the ventral edge of the keel to the posterior extremity, five inches five lines. 



Pleurorynchus giganteus. M'Coy. (PI. IX. fig. 1). 



Sp. Cli. — Cordate, obtusely pointed in front, very much depressed, posterior side suddenly contracted, 

 very short, rounded, gaping ; marginal keel of the anterior side long, thin, simple at the edge ; anterior face 

 conoid, nearly smooth, rising regularly from the margin to the base of the anterior tube, which rises abruptly 

 at a considerable elevation from the beaks ; surface nearly smooth, obsoletely striated transversely ; the contracted 

 posterior end marked with strong ridges from the beak. 



This is one of the largest known species of Pleurorynchus. Length from the posterior extremity to the 

 beaks about one inch four lines, from the same point to the extremity of the front margin four and a quarter 

 inches, width of the keel three and a half inches. 



Pleurorynchus Hibernicus. Phil. 



Cardium Hibernicum. Sow. Min. Con — Pleurorynchus Hibernicus. Phil. Geol. York. 



Sp. Ch. — Horsehoof-shaped, anterior end truncated, nearly flat, rising abruptly into a slender, lengthened 

 tube near the hinge ; the edge which bounds the anterior face is produced, parallel to the body of the shell, so 

 as to form a deep shelly border to tlie anterior end ; body of the shell conical ; posterior end cylindrical, produced. 



This species, from its resemblance to a horse's hoof, is well known to our quarry men by the name of 

 " foal's foot," and is much prized from the ready sale they get for them. 



.The tube which issues from tlie anterior side is as thick as a crowquill, and about four inches long ; the 

 posterior end forms a much thicker tube about two inches long, and gaping at the end hke a Pholas, the por- 

 tion of the shell which projects all round, beyond the margin of the truncated anterior face, is about as deep as 

 from the same point to the base of the posterior tube ; it is usually broken off"; the surface is delicately striated ; 

 the anterior face is nearly smooth, except in the centre, where there are about a dozen concentric ribs. Length 

 two inches three lines. 



Pleurorynchus inflatus. M'Coy. (PI. IX. fig. 2). 



Sp. Ch. — Body of the shell very gibbous, regularly ribbed from the beak; anterior face convex, inflated, 

 smooth, or marked only by lines of growth, separated from the body of the shell by a short, obtuse keel ; ante- 

 rior tube very long, cylindrical, smooth. 



