BRACHIOPODA. 381 
valve with a bi-lobed cardinal process, between the dental 
sockets, and four depressions for the adductor muscles. 
Ventral valve. Fig. 184. Dorsal valve. 
Interior of 8. rhomboidalis, var. analoga, Carb. limestone (after King). 
e, foramen ; ¢, teeth; o, ovarian spaces; 0, brachial pits ? 
There are no apparent brachial processes in the dorsal valve 
of Strophomena, and it is possible that the spiral arms may have 
been supported at some point near the centre of the shell (0) as 
in Productus; S. rhomboidalis occasionally exhibits traces of 
spiral arms, in the ventral valve. 
S. latissima, Bouch., has plain ee), 
areas, like Calceola. B 
The valves of the Strophomenas 
are nearly flat until they approach 
their full growth, they then bend 
abruptly to one side; the dorsal 
valve becomes concave in S. alter- 
nata and rhomboidalis, whilst in 
eee ciple meus ain 
: aie < : A, hinge-areas; v, ventral; p, interior 
tions are not even sub-generic. of dorsal valve. 
Fossil, 129 species. Lower Silurian—Carb. North America, 
Europe, Thibet. 
S. demissa, Conr. (Stropheodonta, Hall), S. Dutertrii, and 
several other species have a denticulated hinge-lne. 
Sub-genera ? Leptena (part), Dalman. I. transversalis, 
Fig. 185. (Plectambonites, Pander.) Valves regularly curved; 
dorsal concave, thickened, muscular impressions elongated. 
Fossil, 41 species. Lower Silurian—Lias. North America and 
Kurope. The lias Leptenas resemble Thecidia internally ; they 
are free shells, with sometimes a minute foramen at the apex of 
rhe triangular deltidium; L. liassina, Pl. XV., Fig. 25. 
Koninckia, Suess. Producta Leonhardi, Wissm. (P. alpina. 
Schl.), Fig. 186. Trias, St. Cassian. Shelt orbicular, concayo- 
' conyex, smooth; valves articulated ? closely appressed ; ventral 
valye conyex, dorsal concaye; beak incuryed, no hinge-area 
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