118 
On Perna quadrata, Sow. By Joun Lycert, Esq. 
Reap 30TH January 1855. 
THE present notice of a fossil shell; which has already been 
figured and described, requires some explanation. 
The Perna quadrata of the ‘ Mineral Conchology,’ t. 490. f. 2, 
represents a very inequivalve Perna ; but as the specimen figured 
appears to have been somewhat imperfect, and as it was placed 
by the artist in an unfortunate position and is seen only from 
a single point of view, it affords a very insufficient aid to a de- 
scription which is substantially correct as far as it refers to the 
only specimen which appears to have been at the disposal of the 
author. With such an illustration it will not afford surprise to 
find that Phillips in his Geology of Yorkshire, t. 9. f. 24, repre- 
sented a second and very different shell under the name of Perna 
quadrata ; and as the latter work contains no descriptions of spe- 
cies, Goldfuss was in turn also misled to figure a third Perna 
distinct from both the others under the same name (Petrefacta, 
t. 108 ); upon the same plate however is Perna rugosa, which is 
identical with the quadrata of Phillips ; the latter is an equivalve, 
squamous, thick shell, well known to collectors of British Inferior 
Oolite fossils. There is another inducement to acquire a correct 
knowledge of the original Perna quadrata, inasmuch as the spe- 
cies is a very remarkable one, constituting a departure from the 
typical forms of the Perne, and approaching to others of the 
kindred genus Inoceramus. The diagnosis of this shell in the 
‘ Mineral Conchology’ is as follows :—“ Quadrilateral, one side 
shorter than the other three ; valves gibbose, unequal, the shorter 
side very concave, bounded by two obtuse carinz.” 
The figure in the ‘ Mineral Conchology’ has the right or 
flattened valve facing the spectator ; the contour of the larger or 
convex valve therefore is not seen : the shell is not placed upright 
upon the page, the lower border forming the right-hand side of 
the figure: even the outline is not perfect, as there seems to be a 
portion of the lower border wanting, and thus forming an angle 
at its anterior extremity, which would be rounded were that part 
entire. 
The typical Perne are equivalve or subequivalve ; their fibrous 
tests are squamous externally, and acquire great thickness with 
