Vol. 6S.'] SUCCESSION IN THE NORTH-WEST OP ENGLAND. 569 



of short, blunt, and curved spines cluster on the ears, and are" 

 continued as a double row aloug the hinge-line. Spines are also 

 given off sparingly from the skirt, which is slightly undulating. 



Horizon and localities. — This form appears to be confined 

 to a definite band at the base of the Semimda-gregaria Sub-zone. 

 Friar's Bottom, Ravenstonedale District ; Fawcett Mill, Shap 

 District. 



Prodttcttjs aff. globostjs. 



This form resembles Pr. glohosus closely, in size and in general 

 appearance. It differs, however : (1) by the more clearly-defined 

 character of the ribs, which are both coarser and more clearly cut; 

 (2) by the more pointed and less globose character of the visceral 

 disc, from which results the fact that the intercalation of fresh 

 ribs takes place much farther from the umbo, in the region near the 

 anterior portion of the visceral disc. 



Only two specimens of this form have been met with, at the base 

 of the Lower Bibunojohjllum Sub-zone, in the Bryozoa Band, east of 

 lioman Fell, in the Pennine District. 



Productijs eottjndtts, sp. nov. (PI. LI, figs„ 3 a & 3 6.) 



Pedicle - valve. — Besembles Product us glohosus in general 

 appearance, but differs in the following points : — 



1. Shell slightly larger. 



2. The greater width of the shell across the region near the anterior end of 



the visceral disc, in which region, as also over the skirt, there is in some 

 specimens a slight tendency to a sinus. 



3. The coarse character of the ribbing. Seventeen ribs in 10 mm. 



4. The continuation of the wrinkles over the visceral disc, producing a 



slightly scrobiculate appearance in that region. 



5. The presence of fine concentric lines of growth, which are specially 



conspicuous on the skirt. 



Horizon and localities. — Abundant in the Productus- 

 glohosus Band at the base of the Semimda-gregaria Sub-zone. 

 Friar's Bottom, Ravenstonedale District ; Fawcett Mill, Shap 

 District. 



Prodtjctus cf. GiGANTETJs Mart. 



This form is very close to, if not identical with, that figured 

 by Davidson.^ It differs from the typical Pr, giganteus of Martin 

 by its smaller size, more globose form, and slight development of 

 ears. The coarse ribbing characteristic of the type-species is but 

 faintly developed, and the convex valve has the shell greatly 

 thickened in the neighbourhood of the hinge-line. The shell 

 resembles rather closely in external appearance well-grown ex- 

 amples of Daviesiella llangollensis ; but internal casts of the convex 

 valve show conspicuous eminences, representing the cavities for 

 the fleshy arms shov/n in Davidson's figure. These casts, indeed, 



1 • Brit. Foss. Brachiop.' Monogr. Pal. Soc. vol. ii (1858-63) pi. xxxvii. 



