part 2] 



smiKGOTHVltlS AND SPIBIFEBJNA. 



199 



Fig. -4. — The profiles 0/ Tylothyris, Spiriferina, ff«<#Punctospirifei\ 

 (The broken lines in b and h represent the contour of the 

 interior of the shell.) 



a= Tylothyris laminosa mut. ji. 



b= Tylothyris laminosa mut. 7. 



c = Tylothyris, between laminosa and subconica (C-S). 



d = Tylothyris subconica castletonensis (D). 



e = Tylothyris subconica subconica (D). 



f = Spiriferina inscnlptu . 



g = Spiriferina octoplica fa . 



h = Punctospirifer scabricosta. 



Mutations of Tt/lotJti/ris laminosa. 



The species in its typical condition is characteristic of beds of 

 Z.-C, age, but it is also represented in K and in Z r 



(a) Tylothyris laminosa mut. /3 includes small specimens 

 from K and Z,, in 'which there are indications of all the essential 

 characters of the species. 



Description. — T. laminosa mut. /3 differs from the typical 

 form of the species in the following respects : — The shell is smaller 

 and the area less elevated, the cost;e are more sharply defined, and 

 the development of the apical callosity is less pronounced. The 

 dimensions of an average specimen are as follows : — width along 

 hinge-line, 24< mm. ; height of area, 6 mm. ; length of brachial 

 valve, 12 mm. 



Horizons and localities. — lv, in the Upper Neath Valley, 1 

 K at Mitcheldean and Burrington, 3 and rarely in Z, in the Mendip 

 area generally. 



1 Collected by the late Mr. C. H. Cunnington. 

 - Vaughan [28] p. 384. 



Q. J. G. S. Xo. 302. p 



