THE NAIADES OF MISSOURI IgI 
cavities; hinge teeth usually flattened, very wide and heavy: 
nacre bright pink; epidermis leathery-red with rays on anterior 
part of shell ... 
MISCELLANEOUS REMARKS:—This form of catzllus is the most 
common of the Pleurobemae in the Osage—Gasconade system and 
is not found any where else in the state. This ‘“‘solida’’ variety 
is characteristic for its small, solid, subglobular shell, with a 
more rounded posterior end and less compression for the posterior 
half than in typical caiillus. The radial furrow of the type species 
(obliquum) is entirely lost. ‘The only difference between this form 
in the two basins (that of the Osage and Gasconade) is in that of 
nacre-color—the Osage never varying from pink and the Gasconade 
shell always with white-nacre. The almost endless inter-grada- 
tions for obliquum and catillus seem to be the general rule rather ~ 
than exception, but here in Central Missouri the variety herein 
described is predominant. Another form occasionally met with in 
the Osage and grading in between this subspecies and catillus is 
one that comes near to fulgidus of Lea, but it would not be listed 
on account of its rare occurence and doubt whether it should be 
really separated from this variety, obliquum caitllus. Hundreds 
of individuals of this form were examined daily throughout the 
entire month of July, when it was in the height of its breeding season, 
to find it only gravid (without exception) in its outer gills. It is 
found to be tachytictic. Perhaps the best idea can be otbained, 
concerning the difference of the Central Missouri catillus from 
that of South Missouri, by comparing two average measurements 
of mature shells given in the following: 
Sex Length Height Diameter Locality 
Cu S77 Of en ee AT . (White R., Hollister)—S. Mo. 
Cu SAS aX AAD pr EZO (Osage R., Warsaw)—Cen. Mo. 
In both the radial furrow of typical catzllus is effaced. The 
measurement of the latter removes it so far from the type species 
that probably a good species might be made out of it. 
Pleurobema obliquum coccineum (Conrad). 
(“Pink Pig-toe,’’ ‘“Round Pig-toe,” “Flat Nigger Head.’’) 
PLS ENG ae 12S. OL An aw ORE Ll), 
1836— Unio coccineus Conrad, Monog. III, p. 29, Pl. XIII, fig. I. 
1839—Pleurobema obliquum coccineum (Conrad) Ortmann, Pr. Am. 
Ams Phil) Soc. -Lil- pp: 287—390. 
