UNIONIDZA. 23 
Triconopus, Sandberger, 1864. 
Distr.— T. Sandbergeri, Alberti (exxi, 29, 30). Triassic. 
Shell like Cardinia, hinge also nearly the same, except that 
the posterior lateral tooth is very strong, single in the right and 
double in the left valve; anterior lateral tooth short and small ; 
cardinal teeth distinct; muscular impressions elongated and 
attenuated above. Closely allied to Cardinia. 
CarpintA, Agassiz, 1841. 
Etym.— Cardo-inis, a hinge. 
Syn.—Thalassides, Berger, 1833 (no description). Sinemuria, 
Christol. Pachyodon, Stutch. Ginorga and Dihora, Gray. 
Storthodon, Brown. 
Distr.—Fossil, 71 sp.  Silurian—Inferior Oolite; Europe, 
along with marine shells. C. Listerti, Sowb. (exxi, 31). 
Shell trigonal or ovately elongated, compressed, inequilateral, 
with pointed, not very prominent beaks, these being close 
together; hinge with one cardinal tooth in the right valve and 
two small ones in the left, and one remote lateral tooth on either 
side in each valve; muscular impressions deep, rather small, and 
situated next to the lateral teeth; ligament of moderate strength, 
but long. 
This genus is sparingly (and rather doubtfully) represented in 
Silurian rocks; its maximum of development falls in the Lias, 
and it disappears with the close of the Jurassic period. 
( Naiades.) 
Famity UNIONID#. 
Shell usually regular, equivalve, closed; structure nacreous, 
with a very thin prismatic-cellular layer beneath the epidermis ; 
epidermis thick and dark; ligament external, large and prom- 
inent; margins even; anterior hinge-teeth thick and striated, 
posterior laminar, sometimes wanting ; adductor scars deeply 
impressed ; pedal sears three, distinct, two behind the anterior 
adductor, one in front of the posterior. 
Animal with the mantle-margins united between the siphonal 
orifices, and, rarely, in front of the branchial opening; anal 
orifice plain, branchial fringed; foot very large, tongue-shaped, 
compressed, byssiferous in the fry, and sometimes in the adult ; 
gills elongated, subequal, united posteriorly to each other and 
to the mantle, but not to the body; palpi moderate, laterally 
attached, striated inside; lips plain. Sexes distinct. 
The river-mussels are found in the ponds and streams of all 
parts of the world. Inthe old world the species are comparatively 
