﻿Vol. 64.] IN THE CARBONIFEEOUS KOCKS AT LOTJGHSHTNNY. 467 



Skerries sequence, and characterizes the same level in the Midland 

 and Northern areas. 



The figure shows the common form of the Irish specimens. 



Productus striatus obviously belongs to the group of Fr. corru- 

 (jatus, with which it agrees in the type of ribbing and in the rapidity 

 with which it narrows towards the beak. 



Peoductus, sp. nov. 



Productus cL fimhriatus, 'Rush paper' p. 308 & pi. xxx, fig. 6. 



Specimens of this form are not uncommon in Lower and Middle 

 P, but are too fragmentary to permit a complete definition of the 

 species. 



The pedicle-valve has the form of Productus fimhriatus. The 

 ornament consists of concentric bands, practically smooth between 

 the erect pustules. 



The brachial valve is deeply grooved concentrically, and the 

 intermediate ridges bear scattered crenulations, more numerous at 

 the cardinal angles. The interior of the brachial valve has often 

 a puzzling resemblance to a pedicle-valve of Productus rugatus 

 (see Davidson, pi. xli, fig. 6). 



Spiriferids. 



Spirifer. 



Spirifer bisulcatus, var. : cf. Sj). integricosta. (PI. L, figs. 3 a 



The number of variants from the typical form of Sj). bisulcatus, 

 J. Sow., is, in Dg, very large and doubtless dependent, to a con- 

 siderable extent, upon the great variation of conditions which 

 marked that phase. 



The variant here figured has a transverse form, few strong simple 

 ribs separated by deep furrows, and a prominent truncated mesial 

 fold divided by two grooves near its margin. The area is broad 

 between the beaks. 



The peculiarity of this variant lies mainly in its shape : the left- 

 hand side being usually rounded, and the right-hand side square, 

 with a consequent shortening of the area on the left-hand side. 



The resemblance to Sp. integricosta is merely apparent, and is 

 limited to the division of the fold and the shortening of the hinge- 

 line. 



This variant occurs in Lower P somewhat plentifully; it is 

 interesting to note that, at precisely the same level in Nidderdale, 

 near Pateley Bridge, a form of Spirifer bisulcatus, having the same 

 ribbing and fold, occurs, in which the cardinal angles are produced, 

 unequally on the two sides, into long spines. 



