462 B. ETHERIDGE, JTJN., ON A LOWER-CARBONLFEROUS PRODUCTUS. 



present fossils might either be the young of P. longispinus, Sow., or 

 P. Wrightii, Dav., and recommended careful observation as to the 

 other species of Productus found in company with the present form. 

 Mr. Bennie, when collecting the disintegrated shale from which the 

 specimens were obtained, observed that the only other Productus 

 present in any thing like appreciable quantity was P. longispinus, 

 Sow., with this peculiarity, however, that at one of the localities 

 (East Barns) P. longispinus was very plentiful and the adherent 

 form correspondingly rare, whilst at another locality (Skateraw) the 

 proportions were just reversed. The characters in which the adhe- 

 rent form differs from P. longispinus, Sow., are the following : — The 

 ornamentation of the shell is concentric and not longitudinal ; there 

 is no trace of a sinus in the ventral valve, but a strong mesial ridge 

 in the interior of the dorsal valve extending to the front, which does 

 not appear to be so well marked in P. longispinus ; the upper por- 

 tion of this mesial ridge splits into two, leaving a space between, 

 which is not the case in P. longispinus. The adductor impressions 

 of the latter are situated much higher up under the cardinal process 

 than in the present instance (fig. 23). Lastly, there is a good deal 

 of difference in the distribution of the spines, and in the relative 

 convexity of the valves. 



The division which takes place in the mesial ridge of the dorsal 

 valve (6, fig. 21) appears to resemble that figured by Mr. Davidson 

 in Productus scabricidus, Martin*; but I think it is unnecessary in 

 this case to carry the comparison further. 



The concentric wrinkles or corrugations are sharper and more 

 widely separated than those of Productus undatus, Defrance ; and 

 there is no trace in the adherent form of the fine longitudinal striae 

 of that species. 



The affinities with P. Wrightii, Dav., are much closer than in any 

 of the foregoing cases. In both shells the ornamentation is con- 

 centric, although apparently more regular in P. Wrightii. The 

 size of the two forms is much more approximate, especially one of 

 Mr. Davidson's figures f ; and the spines in the enlarged figure of 

 the same author have much the appearance of those of the adherent 

 form, although fewer in number. At the same time there do not 

 appear to be any along the hinge-line of P. Wrightii ; and, so far as 

 my own observation has gone, there is no trace of the marginal frill 

 of the latter in the present instance. 



I do not feel justified in immediately publishing this form as a 

 distinct and undescribed species, but would rather await the opinion 

 of those more intimately acquainted with the structure and variations 

 of the genus Productus than I can pretend to be. At the same time, 

 should further researches prove these little shells to be worthy of 

 separate specific recognition, I do not think any name could be more 

 appropriate than one which would express the peculiar habit for 

 which they are remarkable — such for instance as Productus complec- 

 tens, the embracing or encircling Productus. 



* Mon. Perm. & Carb. Brach. pi. 42. f. 8 a. t Ibid. pi. 33. f. 6. 



