502 R. ETHERIDGE OX ADHERENT CARBONIFEROUS PRODUCTION. 



without leaving any very definite trace of their existence. A much 

 stronger point against the Chonetes -affinity of Fig. 4 lies in the 

 presence of the long spines which protrude from the general surface 

 of the shell and are now compressed along the surface of the Crinoid 

 stem ; for, so far as I know, there is no distinct evidence that Chonetes 

 possessed such spines, but a series of small prickles scattered over 

 the radiating striae of the valves, as in our common C. Lctguessiana, 

 De Koninck*. Nevertheless, in his generic description of Chonetes, 

 Prof. James Hall says, " it has been ascertained that spines some- 

 times occur on the body of the shell "f . Again, there is another point 

 worthy of notice in connexion with the spines in Fig. 4. Speaking 

 of the difference between these structures in the two genera Productus 

 and Chonetes, Prof, de Koninck says that, in the former, the spines 

 are long, straight, cylindrical, and open at the extremity, but in the 

 latter they are usually short, recurved, pointed, and closed X '■> now 

 it is quite apparent that of the two the spines in Fig. 4 agree more 

 closely with Prof, de Koninck's definition of those of Productus than 

 of Chonetes. 



The family Productidae consists of the following genera or sub- 

 genera, as the fancy of the reader may induce him to regard them, 

 viz. Chonetes, Aulosteges, Strophalosia y Productus, and Productella ; 

 and it may be roughly divided, for the purpose we now have in 

 view, into two sections, according to the presence or absence of an 

 area and foramen. 



Area and foramen absent. Area and foramen present. 



Productus. Chonetes, Fischer. 



Aulosteges, Helmersen. 

 Strophalosia, King. 

 Productella, J. Hall. 



Granted that the parts I have described in Fig. 4 as the area and 

 foramen are such, we may at once dismiss Productus from further con- 

 sideration, although I do not overlook the fact that an area has been 

 described and figured in some species of the genus § ; still it is the 

 exception and not the rule, and it becomes a question for Brachio- 

 podists to what extent restriction on this point should be carried 

 in the genus Productus. 



I think little need be said as to any resemblance, on the contrary, 

 between Fig. 4 and Aulosteges ; for the very well-marked difference 

 in the form of the area at once separates them. 



* I adopt the name C. Lagnessiana, in preference to that of C. hardrensis, 

 for our common Carboniferous Chonetes, in deference to the opinion of Prof, 

 de Koninck, although I quite fail to appreciate the differences which are said to 

 exist between the two forms. 



t Pal. N. York, iv. p. 152. + Mon. Productus et Chonetes. 



§ P. semireticulatus (Davidson, Mon. Carb. Brach. t. 43. f. 5), P. costatus 

 (Hall, Pal. N. York, iv. p. 149), P. (? Productella) Murchisonianus, De Koninck 

 (Mon. Productus et Chonetes, t. 16. f. 3), P. (? Productella) subaculeatus {ibid. 

 t. 16. f. 4, b), P. horrescens, De Verneuil (Geol. Russia, ii. t. 18. f. 1, a), &c. 



