82 SYNOPSIS OF THE CHARACTERS OF THE 



Pteeonites sulcatus. M-Coy. (PI. XIII. fig. 5). 



Sp.Ch. — Transversely trigonal; anterior end pointed; posterior end broad, subtrancate; a triangular 

 space extending from the liinge-line to about the middle of the posterior end, smooth ; from thence to the front 

 margin, roughened by about thirteen or fourteen rugged, obtuse ribs. 



The strongly ribbed or radiated surface distinguishes this species from the nearly allied Pteronites latus ; 

 the form is almost exactly that of the P. latus, the anterior end being, however, more pointed ; the beaks 

 are exceedingly small. Length six lines, width one inch. 



Pteronites ventricosus. M'Coy. (PI. XIII. fig. 8). 



Sp. Ch. — Transversely elongate, width twice the length, falciform, very gibbous; beaks large, tumid, 

 close to the small anterior end ; hinge-line equal to the width of the shell ; abdominal margin very convex ; 

 surface smooth, or with a few large wrinkles of growth. 



This species is so exceedingly ventricose, that the depth of one of the valves nearly equals its length. 

 Length two lines and a half, width five lines. 



Pterinea. Gold. 



Gen. Ch. — Transversely elongate, oblique, very inequilateral (equivalve ?), hinge-Hne long, forming a 

 short wing on the anterior side, and a large, falciform one on the posterior side ; cardinal teeth from two to five, 

 just under the beak, linear, nearly parallel ; lateral teeth strong, lengthened, double. 



The shells of this genus are much stronger than those oi Avicula, and are, moreover, distingiiished by their 

 strong lateral and cardinal teeth ; they are said to be equivalve, but such as I have seen were not so. 



Pterinea desquamata. M'Coy. (PI. XIII. fig. 2). 



Sp. Ch. — Obhquely ovate, convex ; anterior side small, roxmded ; posterior slope straight, abruptly marked ; 

 posterior wing small, falcate, marked with about seven distant, radiating ridges, the spaces between which are 

 flat and smooth ; there is an intermediate finer rib between each of the two upper pair ; body of the shell 

 radiated with about forty-six smooth, equal, narrow ridges, the spaces between whicli are equal to their own 

 diameter; between each pair there is one fine, sharp rib. 



This approximates to the P. lineata. Gold., but has much finer, radiating ridges, particularly on the pos- 

 terior wing; there are no concentric scales or striae in the present si^ecies. Length nine lines and a half, width 

 seven lines. Collected by Dr. Haines of Cork. 



Pterinea intermedia. M'Coy. (PL XIII. fig. 1). 



Sp. Ch. — Ovato-orbicular, oblique, convex ; anterior ear very small, rounded ; posterior ear two-thirds the 

 length of the shell, pointed ; surface entirely radiated with numerous, close, obtuse ridges, alternately larger and 

 smaller, crossed by rather distant, sharp, imbricating strise. 



This interesting species is closely allied both to the P. lineata, and P. decussate, but differs from the former 

 in being much less oblique, and having a shorter wing, or posterior ear ; and from the latter, in having the strise 

 much finer, more numerous, and unequal in size. Length seven lines and a half, width seven lines. I have 

 seen fragments of individuals half an inch longer than the above. 



AvicuLA. Lam. 



Gen. Ch. — Shell obliquely oval, inequlvalve; hinge margin very much lengthened, and forming narrow, 

 unequal ears ; teeth nearly obsolete. 



