PRODUCTUS. 233 



Productus sinuatus (p. 157). Plate XXXIII, figs. 8 — 11. 



Specimens of this interesting species have been recently found by Mr. Carrington at 

 Wetton, in Staffordshire. 



Productus ermineds, Be Koninck (p. 164). Plate XXXIII, fig. 5. 



This rare species (?) has been discovered by Mr. Carrington in the Carboniferous Lime- 

 stone of Wetton, in Staffordshire. 



Productus aculeatus, Martin (p. 166). Plate XXXIII, figs. 16—18 (19?), and 

 Productus Youngianus, Bav. (p. 167). Plate XXXIII, figs. 21 — 23. 



Mr. Burrow is disposed to consider these two species as synonymous, and believes 

 that there exists every possible gradation from the almost perfect smoothness or transverse 

 lines of aculeatus to the strong ribs of Youngianus ; while Messrs. Young, Armstrong, and 

 some others are of a contrary opinion. Mr. Young observes that if there is such a thing 

 as value to be attached to species of the same genus, that there are good distinguishing 

 characters between each of these species; that he has collected a great many specimens of 

 P. Youngianus out of the Shale and out of the hard Limestone, where the whole of the 

 finer external markings have been stripped off, and that he has never been able to identify 

 it in this condition with any form of P. aculeatus he has ever collected or seen figured ; 

 that in all conditions perfect examples show distinctly- marked ribs, and also that these ribs 

 are not due, as has been sometimes supposed, to the prolongation of the basis of the spine, 

 but that they exist independently of the spines ; that he has in his collection specimens 

 that have more than their usual complement of spines, which are not so distinctly ribbed as 

 some that have many less spines, showing, as in many other species, that spines had 

 nothing to do with the formation of the ribs, the spines having no regular order of posi- 

 tion in the valves, while the ribs, in all the examples that have come under his notice, 

 show a regular order of formation ; that, in addition to this peculiar structure, the 

 general form of the shell would be a good guide in distinguishing the two species, 

 P. aculeatus being a much rounder shell, with broader ear expansions than P. Youngianus, 

 which in all Scotch specimens is much elongated, and with small ear expansions ; that on 

 all his best specimens of Martin's shell there is not a trace of ribs, although the lines of 

 growth are preserved, and he can count from eight to twelve distinct scattered spines on 

 each specimen, while on an average-sized specimen of P. Youngianus there are as many as 

 seventy to eighty spines. Such are the results of Mr. Young's careful examination of 

 many Scottish specimens ; and I must admit that when we look at a tray full of shells 

 agreeing with Martin's type and figure of P. aculeatus (PI. XXXIII, figs. 16, 17, IS, and 



