112 SYNOPSIS OF THE CHARACTERS OF THE 



This sliell lias become celebrated from giving its name to the present genus ; tlie front is produced to a 

 length unusual even in this genus, whence Martin's name; the spines on the sides of the shell, at the base 

 of the ears, are sometimes two and a half inches in length, and curved outwards. The flat, rostral portion 

 of the ventral valve has generally a smooth margin, about a line in breadth. Length two and a quarter inches, 

 width one inch. 



Producta maxima. M'Coy. (PL XIX. fig. 12). 



Sp. Ch. — Twice as wide as long; gibbous; front flattened; beak large, undefined; both valves coarsely 

 striated ; strije slightly waving. 



This gigantic shell is considerably the largest known species of the genus. The hinge-line is wide, the 

 beak very gibbous, but the front is broad and flattened. Width frequently one foot. 



Producta membranacea. PJdl. sp. 



Leptcena membranacea. Phil. Pal. Fos. 



Sp. Ch. — Semicircular, flat; substance of the shell very thin, with numerous close, concentric, undulating 

 wrinkles ; spines few, irregularly placed. 



This delicate species occurs in great abundance in the carb. slate series of Ireland, but the characters are 

 not very decisive, and it seems very nearly allied to the P.frar/aria. 



Producta mesoloba. Phil. 



Producta mesoloba. Phil. Geol. York. 



Sp. Ch. — Subquadrangular, gibbous; front concave, with a central, narrow, convex ridge; surface smooth, 

 transversely wi'inkled at the beak, with large, scattered, adpressed spines. 



The specific name indicates one of the most remarkable characters of this species, namely the mesial lobe, 

 which is situated in the centre of a wide hoUow in the middle of the dorsal valve ; the surface is smooth, except 

 at the beak, where it is concentrically wrinkled ; the sj)ines are large, irregularly jjlaced, and adpressed, so that 

 their points are directed towards the beak. The ventral valve is concave, with a central sulcus, corresponding 

 to the mesial ridge of the dorsal valve ; the hinge-line is a little shorter than the width of the shell, so that the 

 ears are obtuse, angled. Length one inch, width one and a quarter inches. 



Producta muricata. PliU. 



Producta miiricata. Phil. Geol. York. 



Sp. Ch. — Semicylindrical, short, very gibbous, front convex; regularly ribbed from the beak with large, 

 rounded ribs, muricated by strong, regularly-placed spines. 



This species is distinguished from every other by the extreme regularity of its strong, radiating ribs, which 

 are ornamented from the beak to the margin by large, equi-distant, spiniform tubercles, the tubercles of one rib 

 alternating with those of the next ; the ears are short, square, depressed. Length one inch, width the same. 



Producta ovalis. Phil. 



Producta ovaHs. Phil. Geol. York. 



Sp. C/i .^Longitudinally ovate, very gibbous; mesial furrow slight; ventral valve nearly flat; surface 

 with nimierous, undulating, transverse ridges, having numerous, very small spines. 



This rare species is at once distinguished by the length of the ventral valve rather exceeding the width, so 

 as to give a regularly ovate outline ; the number and small size of its spines, and fine, concentric wrinkles, 

 distinguish it from the P. pustulosa, which it most resembles. Length nearly two inches, width one inch seven 

 lines. 



