10 BRITISH CARBONIFEROUS BRACHIOPODA. 



near the middle. In some adult, and in all young shells, the valves are regularly convex, 

 and moderately inflated, but after a certain age a sinus with two lateral ridges is 

 developed, while a mesial depression, with two lateral ridges and a smaller central elevation 

 or rib, exists in the dorsal one, so that this valve towards the front becomes triundate, 

 forming a W-shaped frontal line, of which the central point is either higher or lower than 

 the lateral ones. The ventral valve is deeper and more inflated than the opposite one, 

 the beak rounded and incurved, ridges obscurely defined ; foramen small, oval or circular, 

 and partly surrounded, and separated from the hinge by a small deltidium. Surface 

 smooth, or marked by either few or numerous lines and ridges of growth ; shell-structure 

 minutely perforated. In the interior of the ventral valve there exists two moderately 

 developed dental or rostral shelly plates, while in the dorsal one a short, simply attached 

 loop extends to about one third of the length of the valve. Dimensions variable. Three 

 individuals have measured — 



Length, 7, width 6^, depth 5 lines. 

 5, „ 5, „ 3^ lines. 

 4£ „ 4, „ 3 lines. 



Obs. This shell is extremely variable, both in shape and character, so much so that, 

 to my eyes, certain examples are undistinguishable from others of Martin's T. sacculus, and 

 to which M. De Koninck admits it to be nearly related, but distinguishable in well-grown 

 examples by the triplicated aspect of its smaller valve, as well as by its w-shaped frontal 

 margin. This last appearance is, however, exceedingly variable, for in many specimens 

 the triundate wave is imperceptible, or existing simply in a rudimentary condition. 

 Professor M'Coy seems to have been unfortunate in his researches and appreciations 

 regarding the present form, as appears evident from a glance at p. 412 of the * British 

 Palaeozoic Fossils.' Therein the author refers the shell in question to Terebratula 

 seminula of Phillips, which is not only specifically different, but belongs likewise to another 

 genus ; for, on the admission of Professor Phillips, as well as in the opinion of Professors 

 De Koninck and Morris, T. seminula, Phil, is a true Rhynchonella, while the shell so 

 described by Professor M'Coy, in the work above mentioned, is a Terebratula. In the 

 'Synopsis of the Carboniferous Fossils of Ireland,' p. 158, the same author changes 

 Phillips's name T. seminula into Ter. pisum, but which last is subsequently repudiated in 

 the Cambridge work, the author again returning to that of Phillips. Having, through 

 the kindness of Dr. Griffith, been able to examine the original example upon which the 

 Irish professor had founded his views, it has appeared to me evident that T. pisum, 

 M'Coy, is a Rhynchonella, which either belongs to Phillips's species, or is closely related 

 to that form, for it is similarly plicated, and does not present the appearance of any 

 example of the shell under description, which Professor M'Coy allows to be the same as 

 T. vesicularis, De Koninck, and to which the five specimens in the Cambridge Museum 

 so labelled certainly belong. 



Loc. In England, it is common in the Craven district, as well as in the Yoredale 





