54 BRITISH CARBONIFEROUS BRACHIOPODA. 



tapering, moderately produced and incurved ; area triangular, wider than high ; fissure 

 large, partially covered by a pseudo-deltidiura. The sinus is rather shallow ; commencing 

 at the extremity of the beak ; it extends to the front, and is ornamented by one or two 

 longitudinal ribs on each of its sides. There is also a small hinge area in the dorsal 

 valve. Measurements taken from three specimens have produced — 

 Length 21, width 20, depth 13 lines. 

 „ 20, „ 24, „ 14 „ 



Obs. There is no doubt that the shell under description is closely allied to Sp. pinguis, 

 but it may be distinguished by the shortness of its hinge line and area, the last 

 being much more triangular and higher in proportion to its width than what is found in 

 any of the numerous examples of Sp. pingiiis that have come under my observation. The 

 area in Sp. ovalis is also at times so small and narrow that the fissure occupies more than 

 half of its entire surface. The dorsal valve is likewise generally not so deep or convex as 

 in Sp. pinguis, so that the inequality in convexity of the valves becomes very perceptible ; 

 the mesial fold is also more uniformly convex, with rarely any trace of that mesial 

 groove or depression so prevalent in all specimens and ages of the species last mentioned ; 

 but it must also be remembered, that although the fold is in general evenly smooth, some 

 exceptional specimens possess a tendency to obscure or undefined plication' at all 

 periods of growth. In Sp. ovalis the mesial fold is sharply defined (figs. 20 — 26), while 

 in Sp. integricosta it is always distinctly ribbed, so much so, that in many young shells the 

 position of the fold can hardly be distinguished from the lateral plications of the valves 

 (figs. 13 — 19). All three, Sp. pinguis, Sp. ovalis, Sp integricosta, present the same pecu- 

 liarity of being sometimes longer than wide, and at other times the reverse. And it was 

 from a transverse variety of Sp. ovalis that, in 1844, Professor M'Coy founded his Sp. 

 hemispharica, but which name the author abandoned in 1855. It appears to me also 

 very probable that Sp. exarata, Fleming, belongs to the same type as S. ovalis ; but, 

 as Dr. Fleming's shell was never figured, and that his description " Perforated valve with 

 broad, smooth, flattened ribs divided by shallow narrow furrows ; beak gibbous, incurved, 

 hinge very short," might apply equally well to several other species, I should question the 

 propriety of adopting that name in preference to the well-known one by Professor Phillips, 

 and especially so as Dr. Fleming has further observed that although he has frequently 

 found the perforated valve it was always mutilated and without the other valve, with which 

 he was not acquainted, as will be perceived from the representation of the original example 

 (fig. 24) kindly communicated by the author. Under any circumstance, the extreme 

 tenuity of the area excludes the possibility of its having belonged to Sp. rotundata, Sow., 

 with which it has been erroneously identified. 



Sp. ovalis is not a very common fossil in the carboniferous limestone. In England it 



^ This is also the case with some examples of Sp. pinyuis. 



