President's Address. 71 



plates of Chiton humilis (Kirkby) from the Upper Limestone 

 Series, and Chitonellus Youngianus from the Main Limestone 

 beds. Other additions have been made to the list by Mr J. 

 Thomson,* and again by the before-mentioned authors.*!- In all, 

 three species of Chiton and two of Chitonellus have been recog- 

 nised, but of late a highly interesting siliceous Chiton-hQarmg 

 limestone has been investigated by Mr James Bennie at 

 Dalry.J This deposit has yielded to Mr Bennie, and Mr J. 

 Smith of Kilwinning, nearly a dozen species of Chiton and 

 Chitonellus, irrespective of those previously discovered. Tlie 

 Chitons chiefly belong to the elongated form of the genus 

 which flourished during the Carboniferous period, and probably 

 has relations with the Silurian species for which Salter pro- 

 posed the name Helminthochiton. One or two forms, on the 

 contrary, essentially differ from this. The Chitonelli include 

 some very peculiar, and one or two unique forms, others ap- 

 proach the recent species more than they do the intermediate 

 fossil shells. Mr Bennie's discoveries will be described in 

 the forthcoming part of the Proceedings of the Natural 

 History Society of Glasgow. 



The concluding order of the Gasteropoda we have to notice 

 is the Heteropoda or iSTucleobranchiata. As before stated only 

 two genera need consideration here — Bellerophon and Porcellia. 



Bellerophon is represented in Scotch Carboniferous rocks 

 by no less than twelve species and two varieties, presenting 

 a wide range in form. One of the most characteristic, and, 

 notwithstanding its common occurrence in certain places, 

 least known species is the B. cornuarietis. It forms the 

 British type of Hall's section Bucania, in wdiicli all the 

 whorls are visible and gradually increase in size. The shell 

 is convolute, and the aperture abruptly expanded. In almost 

 every case B. cornuarietis is met with as casts in limestone ; 

 in fact, I do not personally recollect ever seeing one in any 

 other condition. One of the most typical Scotch species of 

 Bellerojjhon is B. Urci, long ago figured by David Ure. 



* Trans. Geol. Soc, Glasgow, 1865, ii., pt. 1, p. 15. 



t Geol. Mag., 1867, iv., p. 340 ("Notes on some remains of Chiton and 

 Chitonclhis from the Carboniferous Strata of York.sliire and the W. of Scot- 

 land"). X Quart. Jour. Geol. Soc, 1847, iii., p. 48. 



