﻿292 DE. A. VAtJGHAN ON THE PAL2EONTOLOGICAL [May 1905, 



medial area. A row of short, curved spines projects from the hinge- 

 line of the convex valve. 



Differences. — Fro in Productus Cora [Dav.] this species is dis- 

 tinguished by the more gradual slope of the sides, the broader and 

 less-arched beak, and the stronger cylindrical rolling of the wings : 

 typical examples are also much more transverse. 



From Productus giganteus this species differs in its smaller size, 

 in the fact that the wings do not project beyond the rest of the shell, 

 in the greater regularity and distinctness of the ribs, and in their 

 conspicuous increase by intercalation, at definite concentric levels. 



Discussion. — Having collected numerous specimens from 

 Mynydd y Gareg (near Kidwelly), the locality from which the types 

 were obtained, and having compared them with specimens from the 

 Bristol area, I am convinced of the absolute identity of the Bristol 

 form with the type. Furthermore, this species abounds at the same 

 horizon (D t ) throughout the Bristol area as at Kidwelly. 



Varieties. — A form, in which the shell is extremely elongated, 

 differs in no other characters, and must be considered as a mere 

 variety. 



The figure (PI. XXV, fig. 5) illustrates a form, from the typical 

 horizon at Sodbury, in which the beak is much narrower and the 

 ribbing much stronger and more distinct than in the type-specimens. 



Productus giganteus (Martin). 



As interpreted in the following figures : — Davidson, ' Monogr. Brit. Foss. 

 Brachiop.' vol. ii (1858-63) pis. xxxvii-xxxviii, & pi. xxxix, figs. 1, 4. 



The characters of most importance are : — The produced and 

 cylindric ally-rolled wings ; the broad beak sloping gradually into 

 the rest of the valve ; the irregular intercalation of the ribs, which 

 are commonly flexuous ; and finally, the transverse form. 



Productus ppnctatus (Martin), Davidson. 



Specimens, apparently identical with Davidson's, op. cit. pi. xliv, 

 fig. 12, have been found by Mr. T. F. Sibly, in S 2 , in the Weston 

 area; I have also seen a specimen, similar to fig. 9 of the same 

 plate, from Black-Bock Quarry, Tenby (S 2 and D x ). A scabriculate 

 mutation, which is almost perfectly convex, with a very narrow and 

 strongly-arched beak, is common in D 2 and Horizon e. 



Productus pustuloses, Phil., Davidson. 



This gens seems to exhibit continuous mutation, but I have 

 collected too little material as yet to speak definitely. 



A form like Davidson's, op. cit. pi. xli, fig. 2, is common in y, 

 at Burrington Combe, and I have collected variants of this gens from 

 Z^ Z„, y, and C. 



'i' 



Productus scabriculus (Martin), Davidson. 



The commonest form in the Bristol area appears to be almost 

 identical with Davidson's, op. cit. pi. xlii, figs. 5 & 6, but the semi- 

 reticulation is usually more strongly marked in our specimens. 



