304 DE. C. A. MATLEY ON BBACHIOPODA [Aug. 19II, 



usually inconspicuous, ridges cross the ribbing, and at intervals are 

 more strongly marked. Forty to fifty, and sometimes even more, 

 costae may be counted around the margin of each valve. 



Pedicle-valve moderately and uniformly convex, deeper than 

 the brachial valve. Beak small ; cardinal area triangular, bent 

 away from the plane of the margin of the valve, and apparently 

 striated parallel to the hinge-line. Delthyrium open in the spe- 

 cimens examined. 



In the interior of the pedicle-valve the hinge-teeth are supported 

 by dental plates which are continued to form a semicircular ridge 

 enclosing a large concentrically-ridged muscular area around the 

 umbo of the valve. This region is crossed by the vascular trunks 

 which extend from the umbo for about two-thirds of the length of 

 the valve. A low rounded elevation occupies the middle of the shell 

 between the vascular trunks, but is not noticeable on the exterior. 



Brachial valve slightly convex, with a low median sinus 

 extending to the front. Beak small. Cardinal area narrow. A 

 low rounded mesial ridge in the interior of the valve bears at its 

 posterior extremity a simple rounded cardinal process. The widely- 

 separated and divergent crura are short and stout. No chilidium 

 appears to be present. Two pairs of elongated muscular impres- 

 sions represent the places of attachment of the adductor muscle. 



Dim en sions. — The largest example collected (a brachial valve) 

 measures 8 millimetres in length by 11 mm. in width, but the 

 majority of the specimens average about 8 mm. in width. 



Locality and horizon. — The lower section on the Shoot- 

 Bough Road, Comley. Abundant as internal and external casts in 

 a band of the Shoot-Rough-Road Flags, at or near the horizon of 

 Taradoxides davidis. 



Observations. — This variety appears to differ from the form 

 described by Linnarsson from the Pamdoxides-forchhammeri Zone of 

 Sweden in the following respects : — 



(a) The pedicle-valve is always deeper than the brachial, whereas, according 

 to Linnarsson, the brachial valve of the Swedish form is the more convex. 



(b) The ribbing is more regular, never exhibiting the wide interspaces 

 figured by Linnarsson (loc. cit. pi. i. fig. 6 c). 



(c) The Shropshire form is smaller, the dimensions being about two-thirds 

 of those of the specimens described by Linnarsson. 



In other respects the forms closely correspond. 



The apparent absence of a deltidium makes the re^rence of this 

 form to the genus Billingsella somewhat doubtful, although with this 

 exception the species has all the essential features of the genotype 

 Orthis jiepina Hall ( = Orthis coloradoensis Shumard). 



Billingsella lindstecemi Linnrs., var. (PI. XXVI, figs. 18 a-19 6.) 



A very similar form is found associated with the above- described 

 variety, but occurring less abundantly ; and it is also found at a 

 different section of the beds, which has not yielded the variety 

 salopiensis. It differs from the last-named variety only in the 



