110 SPECIES OF THE SYSTEMA. 
have agreed admirably with this factitious compound; no 
natural known shell seems perfectly to answer to the specified 
requirements. Upon the whole, however, the P. sinuosus 
(= pusio) of authors (of which there are many loose specimens 
in the cabinet) accords the best with the definition, and Turton, 
Donovan and other British writers argue, with much proba- 
bility, that the two are identical. Perhaps it is better, how- 
ever, in the absence of any positive proof of their identity, 
to refer it to that species with a qualifying “ probably” 
appended. 
Linneus in his manuscript has modified the expression 
“auricula fere unica” into “ auricula altera minuta.” 
The P. pusio of Lamarck, with “radiis trigesimis” is said 
by Deshayes to be a depauperated varius ; it could not well be 
the O. pusio with “radius 40.” Chemnitz and Schréter have 
erroneously considered a Nicobar shell (Chemn. Conch. Cab. 
f. 635) to be a variety of our European one. 
Ostrea glabra. 
The Pecten glaber (Sow. Thesaur. vol. i. p. 58, pl. 18, f. 169 
to 176) has been generally accepted as the representative of 
this species: this recognition is confirmed by the presence of 
many varieties of that beautiful shell; in the Linnean cabinet, 
where they alone, of the several allied species present, agree 
with the definition. The specimen delineated by Regenfuss in 
his second plate not being in accordance with the description 
of glaber, the “t. 2, f. 16” is rightly erased, as a synonym, by 
the younger Linné: his other figure (pl. 1, f. 10) is not so 
unlike the yellow variety. Gualtier’s delineation is far from a 
good one, yet conveys a general idea of the appearance of the 
species. 
Ostrea opercularts. 
The Pecten opercularis (Donov. Brit. Shells, vol. i. pl. 12) 
still reposes in the box marked for this species in the Linnean 
cabinet. ‘Penn. Zool. iv. t. 60, f. 63—List. Conch. t. 190, 
