CRANIADA. 81 
longest diameter 2 lines. We have only seen the upper surface of this small shell, and 
therefore assign its generic name with doubt. It bears some resemblance to P. antiquis- 
sima (‘ His. Pet. Suec.,’ p. 45, t. xii, fig. 10), and may represent that fossil in its young 
state. We have several individuals, all of one size, on the same mass of stone with 
Sp. octoplicatus (?). Loc. Abberley.” 
Subsequently, in 1852, Prof. M‘Coy confounds it with the Schizotreta elliptica, 
Kutorga, which he supposes to be a synonym of Sowerby’s shell, and consequently 
places P. implicata in D’Orbigny’s genus Orbiculoidea. Morris, in 1854 (‘ Cata- 
logue,’ p. 134), commits a similar mistake, for he places this shell with Discina. In the 
second edition of ‘Siluria’ it is properly considered by Salter as a Cranta; and any 
one who has seen bivalve examples of the species would at once perceive that it is not 
a Discina, and that its interior is that of a Crania. 
In a paper “On the Silurian and Devonian Rocks of Nova Scotia,’ by Dr. J. W. 
Dawson, and published by the Natural History Society of Montreal, Prof. J. Hall 
figures and describes a small shell, under the name of Crania Acadiensis. Dr. Dawson 
has sent me an internal cast of this Nova-Scotian fossil, and I find that it certainly belongs 
to the genus Crania; and, indeed, so closely does it resemble our English shell, that 
I feel inclined to add its name to our list of synonyms.’ Prof. Hall states also, at 
p- 250 of the 2nd vol. of his ‘ Paleontology of New York,’ “that his own Ordicula ? 
squamiformis, op. cit., pl. li, fig. 4, and ‘Geol. Report,’ 1843, p. 108, fig. 1, is pro- 
bably identical with Patella ? implicata of Murchison’s ‘Silurian System,’ p. 62, pl. xii, 
fig. 14a. ‘The American shell occurs in the “ Niagara Shale,” and its thin calcareous 
layers, at Lockport, and at Rochester and Sweden in Monroe County. In size and shape 
it agrees with our C. implicata; is said to be very fragile, and is marked by strong 
concentric lamellz ; it is, therefore, probable that when the interior of this shell is seen 
it may have to be included amongst the synonyms of Sowerby’s species. 
Prof. J. Hall further informs me by letter, that, in 1859, he proposed a genus, 
“ Pholidops,” for such shells as Crania (Patella) implicata, Sow.; but I am not quite 
satisfied that it should include the shell under description.” 
Position and Locality. Of this shell I have seen specimens from the Upper Llandovery 
beds of Mandinam, Llandovery; the Wenlock shales of Ledbury ; Wenlock limestone of 
Rock Farm, May Hill; from Wenlock shales near Walsall, and from Upper Ludlow 
rock at Bradnor Hill, Presteign, north-west of Hereford; in the last locality it occurs by 
millions, in the condition of minute internal casts. From Ireland I have seen a specimen 
1 The figure of the Nova-Scotian shell is reproduced in Dr. Dawson’s ‘ Acadian Geology,’ p. 68, 1855. 
2 Genus Pholidops, Hall. ‘Pal. New York,’ vol. iii, p. 489, ‘Shell small, patelliform ; apex sub- 
central, excentric, or terminal. Surface marked by concentric lines of growth, which are more expanded on 
the posterior side, Interior a shallow oval cavity, with bilobed muscular impressions, the margins flattened 
or slightly deflected and entire.” See also ‘Thirteenth Annual Report of the State Cabinet,’ p. 92, 1860° 
Types, P. squamiformis, P. Hamiltonia. 
11] 
