150 BRITISH CARBONIFEROUS BRACHIOPODA. 



centric, undulating wrinkles, larger and deeper upon the ears, while the entire surface of 

 the shell is ornamented by many radiating, longitudinal, rounded striae, which become more 

 numerous towards the margin from bifurcation and interstriation, and from which project, 

 at variable intervals, tubular spines of sometimes considerable length. Dorsal valve 

 moderately concave, following the curves of the opposite one, and similarly sculptured. 

 Dimensions variable, some examples having attained three inches in length, by four in 

 breadth. 



Obs. This species has varied very much in its general shape, and I am disposed to 

 coincide with Prof, de Koninck, while considering P. semireticulatus, P. antiauatus, P. 

 Martini, P. concinnus, and, I will add, P. Scoticus, as simple variations in shape of a 

 single species, and for which the term semireticulatus is here retained. I am also quite 

 ready to admit that, if we examine only typical examples of P. semireticulatus and P. 

 Martini, a certain degree of difference is perceptible, on account of the profile of the first 

 being simply semicircularly curved, while in the second the valves are geniculated ; but 

 these two extreme shapes are intimately connected by insensible gradation, and indeed 

 very often to such an extent that it would be impossible to say to which in particular 

 certain specimens should be referred. In Mr. Salter's opinion, P. costatus sliould also be 

 considered a variety of the species under description ; x and although that learned 

 palaeontologist may be quite correct in his supposition, I do not feel myself at present 

 sufficiently justified in uniting the two under a single denomination. P. sulcatus 

 has, I fear, without sufficient caution been located, by myself and others, among the 

 synonyms of P. semireticulatus, but I am now inclined to consider it a variety of P. 

 costatus, for reasons which will be given hereafter. P. Scoticus, of which I have seen the 

 original type, appears undistinguishable from P. semireticulatus ; and several other so- 

 termed species must likewise be placed under the same denomination. 



The width of the striae, as well as the interspaces between them, vary also according to 

 the specimen, two or more usually occupying the breadth of a line. The larger number 

 are simple, but others bifurcate here and there, and especially so on the lateral portions of 

 the shell ; two or more in rarer cases will also sometimes unite towards the margin so as to 

 form a single rib, while others are due to intercalation. Several ribs at times cluster 

 together so as to produce an elevation, and thus give to the frontal portion of the shell a 

 somewhat grooved or undulated appearance ; and this was particularly the case with the 

 crushed specimen from which Phillips founded his P. pugilis, the original example being- 

 still preserved in the author's collection. In the species under description, the spines are 

 likewise often more numerous and longer in certain specimens than in others, but always 

 most so upon the auriculate portions of the valve, where they do not appear to have been 

 generally disposed in a double row, or rather to have protruded from an elevated ridge, as 

 in P. costatus, and its variety, P. sulcatus. 



1 i 



Quarterly Journal of the Geol. Soc.,' vol. xvi, p. 441. 



