Opercula{?) in Carboniferous Limestone. 27 



copsis. In 1844 Prof. M^Coy noticed that of N. PMllipsii 

 (M'Coj) *, and figured this structure entirely filling-in the 

 mouth of the shell f. Later on the same author stated that 

 the operculum of Naiicopsis differed from that of any of the 

 Naticida3 in being concentric and not spiral:}:. The most com- 

 plete description of the operculum of Naiicopsis yet given is 

 that by Messrs. Meek and Worthen. These authors describe it 

 as thick and shelly, oval or subcircular in form, with a lateral 

 or submarginal nucleus, with an entire absence of a spiral or 

 subspiral structure, and no articulating projection. The inner 

 side presents a distinct reniform scar of attachment, whilst 

 the fine and concentric lines of growth are visible on the 

 outside §. 



Finally, in the British Museum is a fine example of Naii- 

 copsis Fhillipsii, M^Coy {?=N. elliptica, PhilL), with the 

 operculum iti situ, which will be described hereafter; it is 

 the shell referred to by Prof. M'Coyll. 



1. Carboniferous Forms. 



It is quite open to argument whether some of these bodies 

 may not be the otoliths of fishes. Bearing this in mind, I 

 consulted my colleague, Mr. W. Davies, F.G.S., who was 

 kind enough to examine the specimens with me. The result 

 of the inquiry was that, although some bore a striking resem- 

 blance to otoliths, others, on the contrary, appeared to afford 

 evidence of the operculum view. The question even presented 

 itself as to how large a proportion of the bodies found in 

 rocks of a younger age than the Carboniferous, and usually 

 regarded as otoliths, may be the opercula of Gasteropoda of 

 those beds. 



The first form is more or less circular in outline, rounded 

 and thin- edged on one margin, thickened on the other, and 

 produced into a blunted denticulation or two. The centre of 

 one side is somewhat raised above the sharp margin, leaving 

 a flattened zone, and sometimes traversed by a groove or two. 

 This is a common type, and is frequently much worn, when 

 the characters become obliterated. The opposite side is smooth 

 and convex. Lower Carboniferous Limestone group. Law 

 Quarry, near Dairy (PI. II. fig. 1). 



The second variety is small and oval, with a central rounded 

 nucleus, and a notch in the margin opposite, to which the 



* Synop. Carb. Limest. Foss. Ireland, 1844, p. 33. 



t Idid. t. 3. fig. 9. t Brit. Pal. Foss. 1863, fasc. iii. p. 643. 



§ Illinois Geol. Survey Report, iii. p. 3G5. 



II Brit. Pal. Foss. p. 543. 



