* GENERA PENTAMERUS, &o. 
2SG9 
OBSERVATIONS ON THE GENERA PENTAMERUS, PENTAMERELLA, STRICKLAN- 
DINIA, ANASTROPHIA, AMPHIGENIA, RENSSEL2ERIA, etc. 
The Genus Pentamerus was proposed by Mr. Sowerby in 1813, to indi¬ 
cate the peculiar internal structure of P. knightii, which is the type of 
the genus. Dalman,* objecting to Sowerby’s name, on the ground that the 
shell was not five-chambered, proposed the name Gypidia as a substitute; 
but the latter has not been adopted by naturalists. 
Since that time, much information has been obtained regarding the 
disposition of the internal parts of the shells of this genus, through the 
labors of the European palaeontologists de Yerneuil, King, Barrande, 
M‘Coy, Suess, Davidson, Salter and others. In the meantime, however, 
other species have been referred to the genus, which, having the general 
external characteristics of Pentamerus, still possess features that render 
their union with that genus incompatible; and farther study has shown 
the necessity of separating them. Among the European forms which are 
regarded as strictly referable to the genus, are P. knightii ( Sow.), P.vogu- 
licus (deVer.), P.galeatus (Dal'm.), P. sieberi (Yon Buch), P. pelagicus (Bar.), 
and P. optatus (Bar.); while P. oblongus and P. lens have the characteris¬ 
tic features of the genus less conspicuous, the exterior being smooth and 
the form less rotund. Pentamerus liratus andP. microcamerus have a straight 
hinge-line and distinct area. 
In 1859, Mr. Billings proposed the separation of certain forms from 
the typical Pentamerus, under the name of Stricklandia ( Stricklan- 
DiNiAf), which he describes as follows : 
GENUS STRICKLANDIA = STRICKLANDINIA (Billings). 
“ Generic characters. Shell usually large, elongate oval, transversely oval or 
“ circular, sometimes compressed : valves nearly equal ; a short mesial septum 
“ in the interior of the ventral valve supporting a small triangular chamber 
* Petrefacta Suecana, in Konigl. Vet. Acad. Handl., 1827^ 
f In consequence of the name being preoccupied in botany, Mr. Billings has proposed to change 
to STRICKLANDINIA. 
[ Palaeontology IV.] 
47 
