President's Address. 75 



and divided into nnequal portions by a crossbow-sliapcid 

 groove. It is quite possible tliese may be tbe operculum of 

 Jt!nomphahis,dli\\o\v^\ the objects described by Mr F. Smythe 

 as those of the Silurian forms of this genus, and which 

 we definitely know to be such by demonstration, are discoid 

 and flat and marked externally with circular raised lines.* 

 On the other hand, I have myself figured a body from the 

 Upper Silurian beds of the Island of Gothland -f- as the oper- 

 culum of a Euomj^lialus, conical in outline, and much more 

 nearly allied to those of Professor de Koninck. One otlier 

 fact remains to be stated ; so far as I am aware no object 

 resembling the so-called Hypodcma has been met with in 

 British Carboniferous rocks, notwithstanding the prevalence 

 of the Euomphalidse in them. 



The Pteropoda, or Pelagic Mollusca, are represented in the 

 Carboniferous system by only one genus, Comdaria, and one 

 or two species. The shell of Comdaria is straight, four-sided, 

 tapering towards the distal end, and externally ornamented 

 with transverse granulated ridges. In the majority of in- 

 stances the shell is of extreme tenuity, and is usually said 

 to be nonseptate, but two species have been described in 

 which septa or a siphuncle were visible. These are Conu- 

 laria teres (Sby.)J and C. Trentonensis (IIall).§ The first, it 

 may be said with tolerable certainty, is not a Comdaria at all, 

 as was surmised by Sowerby himself. The structure of the 

 second has left the position of Coiiidaria in the Pteropoda 

 open to doubt. So far as I am aware, however, no direct 

 confirmation of this Cephalopod-like structure in Comdaria 

 has hitherto appeared. || The C. teres is a Scotch fossil, and 

 should be found in the Fleming Collection, from which it 

 was borrowed by the Sowerbys for description. It would 

 be extremely interesting to show its true generic relationship ; 

 it will probably be with either Ortlioceras or Cyrtoceras. 



* Proc. Cotteswold Nat. Field Club. 



t Annals Nat. Hist, 1881, vii., t. 2, f. 9. 



X Min. Con., iii., 1820, p. 108, t. 260, f. 1 and 2. 



§ Pal. N. York, i., p. 222, t. 59, f. 4, a,/. 



II Mrs Gray lias lately found a Silurian Comdaria at Girvan, in wliieli botli 

 sipluinclc and septum are preserved. — August 1882. 



