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140 SPECIES OF THE SYSTEMA. 
out as the type of this species. Although there are several 
species of Tichogonia (to which genus, from the “ dissepimento 
albo”’ this mussel clearly belongs) in the Linnean cabinet, they 
are devoid of typical authority, since the presence of the spe- 
cies has not been indicated in the list of its contents. The 
details of the ‘Museum’ demonstrate its identity with one of 
the forms of the shell similarly named in Lamarck’s ‘ Animaux 
sans Vertébres ;) modern research, however, has divided the 
latter into several species. The name bilocularis should there- 
fore more particularly be retained for that which has been indi- 
cated as the more typical form by the paragraph “ color czru- 
leus huic proprius; sunt tamen varietates, &c.” (M. U); this 
character excludes the varieties c. d. of the Lamarckian spe- 
cies. As the number of denticles is now also held of import- 
ance, the “ cardo apice denticulo obsoleto,” strictly interpreted, 
will confine the number to a single one. The only doubt seems 
to rest between Kuster’s 7’. Wiegmanni and his 7’. bilocularis, 
the former of which agrees more precisely with the stated 
number of denticles (may not this character depend upon 
growth ?): strictly speaking, however, neither of the two ex- 
actly harmonises in that respect with the description, for even 
in Wiegmann two denticles are ascribed to one of the valves. 
SMvptilus exustus. 
From the absence of any illustrative engraving which might 
further limit the specific characters, much speculation has oe- 
curred in respect to this species. Four several shells have 
appeared as rival claimants for the name exustus ; a Tichogonia 
(in Born), Modiola sulcata (in Gmelin), Mytilus Magellanicus 
(in Chemnitz), and the shell named Mytilus exustus by La- 
marck. Linneeus. would certainly have included the first of 
these in bilocularis; the two next are coarsely sulcated, not 
merely striated ; but the last agrees admirably with the “‘ minus 
crassa”? and other details of the ‘Museum Ulrice.’ The lo- 
cality “Jamaica” is also correct, and the identification is 
supported by a reference in the copy of the younger Linné to 
“List. Cone. t. 366, f 206,” which is an excellent representa- 
