224 
THE GEOLOGIST. 
numerous but irregular concentric strisc, or lines of growth, which give to the 
shell a somewliat roughened appearance. The interior of the attached valve is 
surrounded by a raised thickened border of moderate width, and upon it 
the tubular shell-structure is sometimes clearly discernible. In each corner of 
the disk, close to Ihc 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 ot the disk two other prominent but 
approximate muscular imjircssions exist, and which are at the same time some- 
what hollowed out along t heir middle. Mr. Hancock attributes the two first- 
mentioned scars to the divaricator, while the central pair ar creferred to the 
occlusor : the other muscular, ovarian, and vascular impressions which should 
exist in the interior were not suflSciently 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 nnder my inspection exceeded seven lines in length by about the 
same in width. 
The mode of existence peculiar to this a& 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 cu-cumstance 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 vnth 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 Bracliiopoda 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 Koninek, he assui-ed me that it 
could not be identified with his Crania (Patella) Bi/ckholtiana , but that it 
might be the same as his Crania ( Orbicula) truncata (P) It was not until I 
had been able to study the original types and other examples of Prof. M'Coy's 
Crania (Orbicula) quadrata (kindly communicated by Sir E,. Griffith) that I 
could identify the Scottish shell with the Irish author's species. 
At Gare, in Lanarkshire, it has been found at two hundred and thirty-nine 
fathoms below " Ell coal ;" three hundred and forty -three at Langshaw Burn ; 
and three hundred and seventy-five at Kilcadzow. It occurs also at Auchen- 
tibber and Calderside, High Blantyre ; Cajiel Rig, East Kilbride ; Brockley, 
near Lesmahago ; and Robroyston, north ot Glasgow. In Ayrshire, at West 
Broadstone, Beith ; Goldcraig, near Kilwinning ; Cessnock, near Galston ; and 
on the bank of the stream Pomillen, near Strathavon. In Renfrewshire, at 
