80 CARBONICOLA, ANTHRACOMYA, AND NAIADITES. 



Interiors normal. 



Hinge-line arched, edentulous, surmounted posteriorly by a longitudinal 

 hollow groove or elongated escutcheon, below which the ligament arises from a 

 faint linear groove on the extreme edge of the shell. 



Dimensions (fig. 29) : 



Antero-posteriorly . . . .25 mm. 



Dorso-ventrally . . . .16 mm. 



Laterally . . . . .12 mm. 



Locality. — Calciferous Sandstone Series, Kilminning and Kilrenny Mill, Fife ; 

 where it occurs at two horizons, one a hard shell bed in large numbers, the 

 other a siliceous limestone with Littorina (?) Scotoburdigalensis twigs of 

 Lepidodendron. 



Observations. — I am indebted to Mr. Kirkby, of Leven, Fife, for the opportunity 

 of studying these shells. They are interesting as occurring very low down in the 

 Carboniferous series, and are probably the oldest form of Carbonicola known if I 

 am right in my determination. Mr. Kirkby tells me that the late Mr. Salter 

 referred them to Anthracosia. In support of this view, the lunule and general shape 

 of the shell are very characteristic of Carbonicola, and I can discover no evidence 

 of the peculiar teeth of Nucula. The shape and obliquity of the lines of growth show 

 a relationship to G. aquilina, the shell of greatest range in this group, but the two 

 forms are easily distinguished. I have visited the locality myself this summer 

 and obtained a number of specimens, some of which showed the interior. The 

 accessory anterior adductor muscle scar is above the anterior adductor, as in 

 other members of this genus. The hinge is without cardinal teeth, but there is 

 an approach towards a flattened hinge-plate seen as an expansion down- 

 wards of the edge of the shell, more easily seen in casts ; the groove for the 

 ligament is apparent, but I have not seen any specimens with the ligament 

 preserved. In the bed at Kilrenny Mill the shell occurs in great numbers though 

 the horizontal distribution seems limited to a few inches, and a mytiliform shell is 

 very abundant, which I expect is the form named by R. Etheridge, jun., 

 Anthracoptera ? obesa ; l but I hesitate to refer it to this genus (Naiadites) because 

 in addition to the striated hinge-plate it possesses a well-marked tooth in the 

 hinge. I would point out that Mr. R. Etheridge, jun., 2 doubtfully refers a shell 

 from the cement stone group of Craiglockhart Hill, near Edinburgh, to Anthra- 

 cosia ? (Unio) nucleus, Brown, to which I have alluded on p. 63, the original 

 locality being Woodhall, Water of Leith, and it is very possible that it and the 

 species under discussion are the same. 



1 ' Quart. Journ. Geol. Soc,' vol. xxxiv, 1878, p. 12, pi. 1, figs. 12 and 13, (14?). 



2 Ibid, p. 16, pi. 2, fig. 20. 



