wees 
2 
REPORT ON THE UNIONDAE OF ST. JOSEPH RIVER 53 
pustules. The anterior portion is quite smooth, the pustules occupy- 
ing the center of the shell from the umbones to the ventral margin. 
The umbones are small, directed anteriorly and marked by heavy 
ridges. The ligament is a dark horn color, long and wide. The 
epidermis varies from a dark yellow to a dark brown. The cardinal 
teeth are single in the right and double in the left valve, flat, 
large and deeply grooved. The lateral teeth are very strong, and 
much striated in older specimens. The anterior adductor muscle 
sear is oval, deeply excavated and markedly striated. The pallial 
line is deeply impressed anteriorly but almost not at all posteriorly. 
The nacre varies between a whitish hue in young specimens to a 
deep purple in older specimens. There is a satin finish near the 
beaks. The space between the pallial line and the ventral margin 
is a dark purple, with a thin white line running along the ventral 
margin. 
Length 75 Height 64 Diameter 44 
118 30 48 
112 90 46 
78 63 36 
120 91 50 
The river area over which collections were made is about six 
miles in length, extending from a point about two miles south of 
South Bend to Bertrand, a village just above the Michigan state 
line. 
She por he Gosee: Aicvea wih Desctinlion of New Seco 
INTRODUCTION. 
For many years I have been engaged in bringing together from 
the rocks of all geological ages containing them from various parts 
of the world, a very large collection of all available species and 
variations of the Genus Airypa, ior the purpose of a monographie 
revision of the group, and jor the further purpose of, in so far as 
possible, ascertaining the genesis oi species of this group. The 
amount and nature of the material and evidence secured has been 
very gratifying; and can not but aid somewhat in the solution 
of at least some of the important questions involved. 
