168 
not to have been of vegetable origin. There is, I think, very little 
reason for doubting its being a bivalve shell ; and its general form 
induces me to place it under this genus. I obtained it at the sale of 
Mr. Strange’s collection ; and am disposed to consider it as remark- 
ably interesting, from the singular markings which it bears. 
XCIV. Modiola. A subtransverse inequilateral bivalve ; the pos- 
terior side being much the shortest, and the beaks lying towards the 
shorter side: the hinge without a tooth, having only a marginal, linear, 
cartilaginal groove : only one muscular impression. 
This genus is exemplified in Mytilus modiolus, Linn. The modiolee 
are separated by Lamarck, from the mytili, on account of their width 
allowing them to be considered as transverse shells, of their beaks 
not terminating the shell, and of their not attaching themselves by a 
byssus, as the muscles do. He figures five species, as found in the 
environs of Paris : M. subcarinata, M. sulcata, M. pectinata, M. 
arcuata, and M. cor data. 
Dr. Woodward describes specimens of this genus, as found in 
Gloucestershire, Catal. p. n. p. 62, No. 660, &c. whence I have 
obtained M. subcarinata. 
XCY. Anodonta. A transverse shell, having three muscular im- 
pressions : the hinge plain, without any tooth. 
Mytilus anatinus is of this genus ; but I know of no fossil shell 
which can be referred hither. 
XCVI. Unio. A transverse shell, having three muscular impres- 
sions : an irregular callous hinge-tooth, prolonging itself on one side 
beneath the ligamental slope, and articulating with that of the op- 
posite valve. 
This is a river shell, which does not appear to be known fossil. 
XCVII. JVucula. An inequilateral, equivalved, subtrigonal bivalve : 
the hinge on a line, bent at an angle formed by numerous, alternately 
inserted teeth ; the beaks approximating, and turned backwards. 
Lamarck divides the Arcce of Linnaeus into threegenera: Area, having 
