224 



THE GEOLOGIST. 



numerous but irregular concentric striae, or lines of growth, which give to the 



surrounded by a raised thickened border of moderate width, and upon it 

 the tubular shell-structui-e is sometimes clearly discernible. In each comer of 

 the disk, close to the posterior inner margin of the raised border, may be seen 

 two somewhat circular, slightly convex, and prominent— but widely separated — 

 muscular scars ; while towards the centre of the disk two other prominent but 

 approximate muscular impressions exist, and which are at the same time some- 

 what hollowed out along their middle. Mr. Hancock attributes the two first- 

 mentioned scars to the divaricator, while the central pair ar eref erred to the 

 occlusor : the other muscular, ovarian, and vascular impressions which should 

 exist in the interior were not sufiiciently defined in the present species to 

 admit of their being accurately described. The interior of the upper or free 

 valve has not been hitherto discovered ; and none of the Scottish specimens that 

 have come under my inspection exceeded seven lines in length by about the 

 same in width. 



The mode of existence peculiar to this as well as to other similarly con- 

 structed species is the cause of the great irregularity in shape assumed by the 

 larger number of individuals ; for it was the habit of the young of this, as well 

 as of other species of the genus, to fix themselve as parasites to all kinds of sub- 

 marine objects, and they were sometimes so numerously and closely clustered 

 together, that their individual regular growth was prevented, from which it 

 can be easily understood that in such cases the animal must have been com- 

 pelled to develope itself in whatever direction it could find available space. 

 When first formed and up to a certain age the shell of the attached valve was 

 exceedingly thin, and adhered so closely to the surface of the object to which it 

 was fixed, as to have reproduced all the inequalities of its surface, but with age, 

 and from the shell acquiring greater thickness, these inequalities were generally 

 levelled. Nor is it an uncommon circumstance to find the roughness or sculp- 

 ture of the object to which the lower valve adhered likewise reproduced upon 

 the outer surface of the upper or unattached valve, in a very similar manner to 

 what we find to be the case with certain species of oyster. 



Although the Crania we are at present describing is far from being un- 

 common in certain Scottish localities, it does not appear to have been noticed here 

 until the early part of 1858, in which year I received from a friend in Carluke 

 several examples of the attached valve clustered round fragments of various 

 species of encrinal stems, and at a subsequent period bivalve and separate 

 valves were obtained in great abundance in other localities in Scotland, attached 

 to the shell of several species of Brachiopoda and other marine bodies. 



It is no easy matter to distinguish certain forms of Crania : several species 

 bear so close a resemblance to one another that I have felt somewhat em- 

 barrassed how to determine that to which the Scottish shell should be referred. 

 Having submitted several examples to Prof, de Koninck, he assui'ed me that it 

 could not be identified with his Crania (Patella) Ri/ckholtiana, but that it 

 might be the same as his Crania ( Orhicula) truncata (?) It was not until I 

 had been able to study the original types and other examples of Prof. M' Coy's 

 Crania ( Orbicula ) qnadrata (kindly commumcated by Sir R. GrijSith) that I 

 could identify the Scottish shell with the Irish author's species. 



At Gare, in Lanarkshii-e, it has been found at two hundi-ed and thii'ty-nine 

 fatlioms below " Ell coal ;" three hundred and forty-three at Langshaw Eurn ; 

 and three hundred and seventy-five at Kilcadzow. It occurs also at Auclien- 

 tibber and Calderside, High iBlantyre ; Capel Rig, East Kilbride ; Brockley, 

 near Lesmahago ; and Robroyston, north of Glasgow. In Ayi'shire, at West 

 Broadstone, Beith ; Goldcraig, near Kilwinning ; Cessnock, near Galston ; and 

 on the bank of the stream Pomillen, near Strathavon. In Renfrewshire, at 



shell a somewhat roughened 



The interior of the attached valve is 



