110 SYNOPSIS OF THE CHARACTERS OF THE 



Producta hemispheeica. Sow. 



Producta aiirita (pars.) P/iil. 



Sp. Ch. — Sliell hemlsplierical ; ventral valve very concave ; radiating strise close, obtuse, smooth, without 

 spines ; hinge-line equal to the width of the shell. 



In this species the ventral valve is almost as concave as the dorsal is convex, so that there results between 

 them an exceedingly small space for the animal ; tlie ears are short, convex, rounded ; the strise are equal, close, 

 and obtusely rounded; the P.personata, Sow., is probably the internal cast of this species. Size very variable, 

 length from one and a half to three inches. 



Producta intermedia. M'Coy. (PI. XX. fig. 4). 



Sp. Ch. — Transversely elliptical; no dorsal furrow; gibbous near the beak; with about twelve narrow, 

 concentric sulci ; the intermediate broad ridges are flattened, with three rows of small spines, in quincunx ; 

 deflexed, front broad, forming rectangular ears at the sides ; very finely striated longitudinally. 



This curious shell forms a connecting link between the genera Producta, Auct., and Leptayonia, M'Coy, 

 tlie portion near tlie beak is a perfect Producta, and miglit be compared with the P. punctata, while the nearly 

 smooth, deflected front reminds us at once oi Leptagonia. Length one inch eleven lines, width one inch six 

 lines ; tlie flat, concentric ridges are about a line in width, but become narrower towards the beak. 



Producta interrupta. Sow. sp. 



Lepteena interrupta. Sow. Geol. Trans. 



Sp. Ch — Semicircular, gibbous; hinge-line equal to the width of the shell; surface with about twelve 

 rounded, concentric wrinkles, crossed by strong, radiating striae from the beak. 



The most peculiar character of this little species is the interruption of the longitudinal strias by the concen- 

 tric wrinkles, giving them a fringed appearance. Length seven lines, width eight lines. 



Producta laciniata. M'Coy. (PL XX. fig. 12). 



Sp. Ch. — Nearly semicircular, length one-sixth less than the width ; hinge -line rather less than the width 

 of the shell ; moderately convex ; beak small, prominent ; ten or twelve rounded, concentric wrinkles, fringed 

 on their marginal declivity with close, regular, lengthened sjDine bases. 



This rare species bears some resemblance to the P.fimhriata, Sow., but the convex valve of the present 

 shell is nearly as flat as the small valve of the P.Jimhriata ; the general form is more transverse, depressed, 

 and the beak is greatly smaller ; the number of concentric ridges is greater, and they are more closely and re- 

 gularly fi'inged, with smaller spines, wliicli latter arc also set on the marginal, instead of the rostral edge of the 

 wrinkles. Length eleven lines ; width one inch one line. 



Producta latissima. Sow. 



Productus latissimus. Sow. Min. Con. — Producta latissima. Phil. Geol. York. 



Sp. Ch. — Hinge-line very wide; beak much curved, but not large or prominent; ears involute, not 

 distinguished from tlie body of the sliell ; very coarsely striated from the beak ; spines niuiierous, very small. 

 Length one-third the width. 



The margin curls inwards, so as to give a fusiform appearance to the Vhole shell, when young, but with 

 age it becomes nearly hemispherical, the surface assumes a ridged appearance, and the stria; branch and become 

 finer, the whole shell resembling the P. r/igantea, which it sometimes nearly equals in size ; it is distinguished, 

 however, by its smaller, and much less prominent beak. The strias are very thick and distinct for about three- 

 fourths of an inch from the beak, when they suddenly divide into a great number of smaller, flexuous ones, as 



