Stuiatj:. 



180 BRITISH CARBONIFEROUS BRACHIOPODA. 



nature of the longitudinal ribs which ornament the surface of all the species, with the excep- 

 tion of a single one, wherein these are replaced by concentric plaits." In Great Britain this 

 last-named shell has not been hitherto discovered, but another, which is entirely smooth, 

 has been obtained, so that the British species can be divided into two groups, which we will 

 distinguish as follows, and to which we have added the probable synonyms. 



< C. comoides, Sowerby. 

 C. papilionacea, Phillips = C. multidentata, M'Coy = C. papi/racea, M'Coy ? 

 1 C. Dalmaniana, De Koninck. 



C. Hardrensis, Phillips = C. sub-minima = C. gibbervla = C. sulcata? = Cvolva? 

 = C. perlata? M'Coy = C. laguessiana ? De Koninck. 

 s C. Buchiana, De Koninck = C. crassistria, M'Coy. 

 L.eves. C.polita, M'Coy. 



Uncertain species? C. tuberculata and C. serrata, M'Coy. 



Although my distinguished friend has considered the arrangement, the number, and 

 nature of the longitudinal striae as the best means or character to be used in the discrimi- 

 nation of the species, I have not always found them sufficient, on account of the extraordinary 

 variability in this particular which almost every specimen has presented not only at different 

 stages of growth, but in shells of similar dimensions, and I believe that we will find the 

 interior details in each of the species to be somewhat different, and a character of greater im- 

 portance even than that of the exterior, as may be noticed in those of which we have been 

 so fortunate as to procure specimens ; and, indeed, in so difficult a matter every point, both 

 exterior and interior, will require to be carefully examined and compared before a correct 

 determination can be arrived at, and surely the difficulty will be great indeed, and even 

 insurmountable, in those cases where the so-termed species have been fabricated from a 

 crushed or imperfect fragment of a single valve ! 



ClIONETES COMOIDES. PI. XLV, fig. 7 (1 to OP). 



Puode'CTUS Comoides, J. Sow. Min. Conch., pi. 329, April, 181G. 

 Chonetes De Keyserling. Reise in das Petschora-land, pi. vi, fig. 1, 



1846. 



— — Be Koninck. Monographic du genre Chonetes. pi. xix, fig. 1, 



1817. 



— — Dav. Quarterly Journal of the Geol. Soc., vol. x, pi. viii, fig. 1, 



and 2—8? 1853. 



Spec. Char. Shell large, transversely semicircular, concavo-convex ; hinge line straight, 

 as long or a little shorter than the greatest width of the shell ; valves strongly articulated 

 by the means of teeth and sockets. Ventral valve convex, beak more or less developed and 

 incurved, but not overlying the cardinal edge. Dorsal valve concave, following the curves 

 of the other. Each valve is provided with a subparallel area of greater or lesser width, but 



