K. ETHERIDGE OX ADHERENT CARBONIFEROUS PRODUCTIDJ3. 501 



represent radiating or longitudinal ribs on the exterior of the shell. 

 The spines, under the microscope, appear to be of the regular Pro- 

 cluctus type. 



4. As to the identity of the Specimens. 



Eeturning to that first described, Figs. 2 & 3, we see that for pur- 

 poses of identification we can rely only on the form, so far as it is pre- 

 served, the arrangement of the spines, and the nature of the ornamen- 

 tation. Taken as a whole, these characters, in this particular case, are 

 decidedly those of Chonetes, although the first and last are applicable 

 to both Chonetes and Productus, but perhaps more to the former 

 than the latter. On the whole I am inclined to regard this specimen 

 (Pigs. 2 & 3) as an adherent form of Chonetes, although, in the absence 

 of any definite trace of an area or fissure, it may be argued this is 

 rather a premature conjecture. Mr. T. Davidson, P.R.S., was kind 

 enough to examine this specimen shortly after it first came under 

 my notice ; and in a letter on the subject, dated 2nd April, 1877, he 

 says, " the little shell in the tube is very interesting, as it shows a 

 small Chonetes grasping a Productus-spme in a very similar manner 

 to what you have described in Productus. I am not, however, 

 quite sure that it is a Chonetes ; it may be a small Productus." 

 Supposing this (Pigs. 2 & 3), for the sake of argument, to be a 

 species of the latter genus, it may be asked, With what species has it 

 the greatest resemblance ? It appears to me that the decidedly 

 Chonetes-like form and longitudinal ribs on the surface of the shell 

 show a tendency towards Productus margaritaceus, Phill., with one 

 of the figures of which, given by Mr. Davidson*, it would probably 

 be found to have a certain general resemblance, could we view the 

 shell from the exterior, laid out before us, instead of in its present 

 position. It must, however, be borne in mind that, if the young of 

 a Productus, its present form represents what would merely be the 

 extreme umbonal portion of a mature shell ; and we must in conse- 

 quence take into consideration the relative proportions of the longi- 

 tudinal ribs of the shell in its present condition and in the older form. 

 In other words, I think these ribs, so far as can be judged from an 

 interior of the shell only, are too well marked or defined to be the 

 incipient condition of any of our Producti, and accord much better 

 with similar structures seen in the genus Chonetes, especially in 

 Chonetes Buchiana, De Koninck, a young condition of which I think 

 it not at all unlikely to be. 



In the second specimen (Pig. 4) we have, to some extent, more 

 definite characters to depend upon. There are hinge-spines, as in 

 the former case, there is fair evidence of an area, and the remains of 

 a fissure of some kind or other (although this has undergone partial 

 mutilation) — all characters which point towards Chonetes rather 

 than Productus ; on the other hand, I can see no trace of articulating 

 teeth, and I have quite failed to trace a continuation of the spines 

 along the area, although I am less inclined to lay stress on this 

 point, as the spines in question are often broken off in Chonetes 



* Mon. Brit. Carb. Brach. t. 44. f. 6 & 7. 



