214 SUPPLEMENT TO THE 



Linnarsson proposes a new genus, Acrothele. " Sliell corneous, composed of several 

 lamina?, the inner smooth and polished, the outermost one rough and opaque. Ventral 

 valve slightly conical, with excentric umbone pierced by a minute foramen, in front of 

 which there are, at least in one species, two small wart-like protuberances. The field 

 between the umbone and the posterior margin is usually a little flattened, thus forming a 

 slight inclination of the false area. Dorsal valve with marginal umbone, consisting of 

 two wart-like protuberances. In the interior of the dorsal valve there are two oblong, 

 diverging, muscular scars close to the posterior margin, and two small, rounded scars 

 near the middle. The muscular scars are separated by a longitudinal ridge " (Linnarsson). 

 Prof. Linnarsson adds also that the most nearly related genera are, he thinks, Oholella 

 and Acrotreta. 



154. Acrothele granulata, Linnarsson. Dav., Sil. Sup., PI. XVI, figs- 29, 80. 



AcEOTHELE GRANULATA, Linn. Bibang till k. Svenska Vet Akad. Handlingar, Band 3, 

 pi. iv, fig. .01 (and 52?), 1876. 

 — — Swanston. Proc. of the Belfast Nat. Field-Club, pi. vii, 



fig. 20, 1876, 1877. 



" Shell almost circular, a little wider than long ; ventral valve very slightly conical, 

 umbone pointed, very excentric, the distance from the front being about four times that 

 from the posterior margin. The shape cannot be exactly defined from the materials 

 hitherto obtained. 



" Of a false area there is hardly more than a slight trace, only a very narrow space 

 between the umbone and the posterior margin showing a slight difference from the other 

 parts of the shell. The anterior part of the valve is depressed. The inner shell-layers 

 are smooth and polished, the outermost one opaque, granulated, and marked near the 

 circumference by concentric lines of growth. The interior is unknown as well as the 

 dorsal valve. The only specimen of the ventral valve measures length 8 millimetres, 

 breadth 9." (Linnarsson.) From the Paradoxides-beds, Oland, Sweden. 



I have reproduced Prof. Linnarsson's description, as our Irish examples agree well with 

 it. The description and illustrations are, however, rather vague on account of the 

 material in his and in our possession being very incomplete. We are still unacquainted 

 with the interior of the valves. 



Acrothele granulata was discovered for the first time in the British Isles by Mr. W. 

 Swanston, who found several casts or impressions of the shell in a black, highly-indurated 

 shale at Coal-Pit Bay, County Down, Ireland. The rock is referable to the Upper 

 Llandeilo, and the shell under description is associated with Acrotreta Nicholsoni and 

 Biscina Portlockii. Our Irish specimen measures 2| lines in length by 3 in breadth. 

 I think the species will be found to occur in Scotland. 



