10 BRITISH PERMIAN BRACHIOPODA. 



The sinus is also sometimes narrow and more suddenly depressed (PI. I, fig. 5 ; and 

 pi. xlii a of King's Monograph), and hardly perceptible in certain middle-aged and young 

 shells. 



The dorsal valve is more or less regularly convex, with a mesial longitudinal elevation 

 extending from the extremity of the umbonal beak to the front, from which the lateral 

 portions of the valve slope more or less rapidly to the margins. External surface smooth &' 

 shell-structure minutely perforated. 



The internal details having been already described under the genus, need not be 

 repeated. The dimensions attained by this species are very variable. 



The largest two British specimens I have seen measured — 



Length 17|, width 15, depth 8 lines. 

 „ 19, ,, 13 lines. 



a. Var. sufflata. Plate I, figs. 8, 9, 10, 11, 15, 16, 17, and 21; Plate II, fig. 2. 



(King's Monog., pi. vii, figs. 1 — 9.) 



Terebratulites sufflata, Schlotheim. Akad. Munch., vol. vi, pi. vii, figs. 10,11, 



1816. 



This shell is smaller, relatively wider, and more inflated than the var. elongata ; ovate ; 

 margins obtuse, and sometimes slightly emarginate in front. The ventral valve is either 

 regularly convex (PI. I, fig. 11), or presents a narrow mesial sinus, which is more or less 

 excavated (PI. I, figs, 16, 17 ; and PI. II, fig. 2) in different specimens, so that the frontal 

 line varies considerably in the convexity of its curve. The dorsal valve is more or less 

 regularly inflated ; surface smooth. Interior exactly similar to that of elongata. In 

 dimensions this variety does not appear to greatly exceed — 



Length 7, width 6, depth 5 lines. 



Professors King and M'Coy are of opinion that this shell should be specifically sepa- 

 rated from T. elongata, as has been already observed. They state that it is smaller and 

 more tumid, with a greater gibbosity, and with more obtuse angles ; the umbone more 

 gibbous and prominent (?), a small definite lobe in the front margin, and corresponding 

 long, narrow mesial sulcus in the ventral valve ; the posterior part of the shell not so 

 tapering, and the sides of the beak more obtusely rounded and less angulated. 



1 In his ' Notes on Permian Palliobranchiata,' published in the ' Annals of Natural History ' for 

 March and April, 1856, Professor King observes that "specimens occasionally occurring at Gliicksbrunn 

 show T. elongata to have been a prettily coloured species ; in one example several dark bands inter- 

 radiating with others of a lighter colour almost continuously from the umbone to the margin, and increasing 

 in width in their forward progress ; in another, the dark bands reduced to dark lines are only developed 

 near the margin." 



