108 SYNOPSIS OF THE CHARACTERS OF THE 



In general proportion tliis exactly resemhles the Productahemispherica, but the large, concentric wrinkles 

 are peculiar and very constant ; the ventral valve is less concave than in that species, and even fragments might 

 be distinguished by the peculiar character of their striae ; these are thick, close together, and slightly rounded or 

 flattened in the Producta hemispherica, but are very sharp and distinct, alternately larger and smaller, and 

 having a small space between them, in the present species. 



Peoducta costellata. M'Coy. (PI. XX. fig. 15). 



Sp. Ch. — Scmicylindrlcal, short, front flattened, sides compressed; surface with strong, radiating ribs, 

 muricated by long cylindrical spines; a semicircular row of large spines on each side of the shell. 



This species bears some likeness to the P. spinosa, but the radiating ribs are greatly stronger, and the front 



is flattened; the present shell has also a semicircular row of large spines at each ear, and the spines of the whole 



Fig. 10. surface are much larger, and more numerous, than in that shell. Its very short hinge-line, pa- 



IJHjK^'^ rallel sides, and coarse muricated ribs distinguish it from the Producta setosa, Phil. Length 



eight lines, width seven lines. 



The internal structure (see fig. 10) is much more simple than of most of the Products; 

 the supports (a a) form but two lobes on each side of the septum. Instead of the numerous 

 complex turns of the corresponding parts in the more typical species ; the cardinal tooth of the 

 ventral valve (b) is large, and distinctly notched ; the muscular impressions (c c and d d) are 

 similar in shape and position to those of the other Producta; the central septum is particularly large. 



Producta Edelbuegensis. Phil. 



Producta Edelburgensis. Pkil. Geol. York. 



Sp_ Ch. — Semicircular, depressed; beak small; ears flattened; radiating striae thick, branching frequently 

 before they reach the margin. 



This curious species is very like old individuals of Producta latissima, but is more depressed ; the beak 

 is also much smaller, and the ears, which in Producta latissima are almost fusiform, are quite flat in the pre- 

 sent shell ; the radiating striae of the Producta Edelburgensis have a peculiar appearance, from being thick and 

 entire, to a short distance from the beak, and then suddenly dividing Into a great number of smaller ones, as 

 they approach the margin ; these ribs are finely striated across, but usually without spines. Length one inch five 

 lines, width three inches six lines. 



Producta elegans. M'Coy. (PL XVIII. fig. 13). 



Sp. Ch. — Shell forming three-fourths of a circle, convex; nine or ten concentric sulci, the rostral edge of 

 the broad furrows between them, with two or three concentric rows of short, deep, undulating scratches, the 

 maro-inal edtre with three or four concentric rows of punctures, set in quincunx; beak small; hinge-line straight. 



This pretty little shell is related more to the young of P.Jimbriata, Sow., than to any other of the genus ; 

 it is, however, much more depressed ; the beak is large and prominent in that shell, but very small in this ; and, 

 finally, the ridges are greatly more numerous in the present species, and punctured on the marginal edge, in- 

 stead of on the rostral, as in that fossil. The ears of the P. elegans are much flattened, the ventral valve simi- 

 lar, but flatter. Length five lines, breadth six lines. 



Producta fimbriata. Sow. 



Productus fimbriatus. Sotc. Min. Con. — Producta fimbriata. Phil. Geol. York. 



Sp. Ch. — SHghtly elongate, rounded, very gibbous ; about seven or eight broad, concentric ridges, each 

 fringed on its rostral edge with a row of lengthened, spine bases; no mesial furrow. 



