152 CARBONICOLA, ANTHRACOMYA, AND NAIAPITES. 



Dimensions : 



Antero- Dorso-ventrally From side 



posteriorly, (greatest length). to side. 

 PI. XIX, fig. 20, measures 50 mm. 35 mm. 30 mm. 



PI. XIX, fig. 19, „ . 45 mm. 30 mm. 23 mm. 



Locality, — Scotland : — Black Band Ironstone, Bankend, Lesmahagow. 



Observations. — lam indebted to Dr J. S. Hunter, of Braidwood, for the loan of 

 and permission to describe and figure these specimens, which are second in size only 

 to N. crassa of the Carboniferous Limestone. These shells can be distinguished 

 from all others by the alternate fluting of the valves at the posterior inferior 

 angle, a character which is not very apparent in young specimens (PI. XIX, 

 figs. 17 and 19), but becomes more developed with age. 



The shape and general appearance of the shell at first suggested a reference to 

 Mr. Etheridge's Anthracoptera obesa, but from this form N. magna is distin- 

 guished by its more obtuse gibbosity, not so nearly central, and the folding of the 

 posterior inferior angle of the shell, a character I have observed in no other 

 species of this genus. 



Mr. Etheridge says that the posterior margin of his shell is sigmoidal, and this 

 is shown only in one of his figures ; but this curve refers to the margin only, and 

 must not be thought to apply to the peculiar crumpling of the posterior inferior 

 angle of N. magna, a character which is shown to be absent in all figures of 

 N. obesa. 



N. magna, occurs at a much higher horizon than N. obesa, having been obtained 

 up to the present time only from the Blackband ironstone, placed, in the 

 * Geological Survey Memoirs,' Explanation of Sheet 23, p. 80, at the base of the 

 middle beds of the Carboniferous Limestone Series. Judging from the Bankend 

 section given at p. 32 of the same memoir, there is only one Blackband ironstone, 

 the position of which is given about the centre of these middle beds ; and at 

 j). 20 the main Lesmahagow gas coal, which is stated at p. 80 to overlie the 

 Blackband ironstone, is again given as follows : 



Upper (! ron j> .... 



' Strata with their coals and clay ironstone 

 Middle Group Main Lesmahagow (las Coal 



, Si rata .... 

 Lower Group .... 



Ft. 



Inc 



. 232, 



5. 



. 188, 



0. 



1, 



10. 



. 165, 



0. 



. 114, 



1). 



