President's Address. 43 



length, and of a coiTcsponding Lroadtli and tliickness. . . . 

 By workmen they are called limestone oysters. I have seen 

 beautiful specimens of this shell in a quarry near Bathgate." 

 I believe this name is still in use for r. giganteus in certain 

 parts of the country. Again, in 1830, a Mr Pu Craig found 

 examples in the Lanarkshire lower limestones with a 

 diameter of 5 or 6 inches.* 



StreptorJiynchus crcnistria nowhere occurs in such quantity 

 or of so large a size as in Scotland. Mr Davidson, records 

 one 3 inches long, by 4-J inches wide.-f- Zingtda squamiformis 

 also grows to a large size occasionally. This is the case in 

 the Lower Blackband ironstone at Fossil, where it occurs in 

 great profusion. X It attains a similar size and profusion of 

 numbers in the Edge Coal series of the Bo'ness coalfield. 



As a last example, we may mention a newly-discovered 

 shell, Discma Craigii (Davidson), which Mr J. Neilson has 

 found in the cutting of the City of Glasgow Union Piailway 

 as much as If inches across. § 



Many interesting facts have of late been brought to light 

 in connection with the perforation of the shell substance, its 

 prolongation into spines, their nature and use, etc. It would 

 take us too long to enter into this subject in detail, and we 

 can only refer those interested to Mr Davidson's " Supple- 

 mentary Monograph," where the various modifications of 

 structure have been thoroughly described. We may, how- 

 ever, mention the following species as presenting, perhaps, the 

 chief modifications of spine structure : Sijirifera Urii (Flem- 

 ing), S. lineata (Martin) (a particularly noticeable modifica- 

 tion from the recent discoveries of Mr John Young), Pro- 

 ductus semireticulatus (Martin), P. pnnctahis (Martin), P. com- 

 plectens (Eth.), Atliyris Eoysii (Leveille), and A. lamcllosa. 



The spinose investment of Productus punctatus was long 

 ago noticed by old David lire, who figured the shell as 



* Trans. Highland Soc, 1839, vi., p. 3G1. 



t Geologist, p. 104, t. 1, f. 7. 



X Young, " Notes on the Occurrence and Kange of Lingula in the Carboni- 

 ferous Series of the West of Scotland " (Trans. Geul. Soc, Glasgow, 1866, ii., 

 pt. 2, p. 144). 



§ Trans. Gcol. Soc, Glasgow, 1877, v., pt. 2, p. 227. 



