TEREBRATULA. MONOMYARIA. "3 
Genus X.— LEPTEN A. — Dalman. 
Generic Character. — Shell equilateral, and inequivalve; 
oue valve being convex for the most part, and very rarely 
somewhat depressed ; its anterior edge rounded, very thin, 
bent downwards, and produced into an irregularly cylin- 
drical form, a little expanded towards its lower edge, 
the opposite valve is usually flat, or slightly concave on 
the outside, with its anterior margin reflected, so that 
its inner edge lies against the inside of the concave valve; 
the cardinal margin is transverse, parallel and linear, some- 
times so much produced on both sides as to give it a 
winged appearance. 
Leptena scarbiculus. Plate VII. fig. 16. 
* No remains of a ligament have been noticed, but there have been observed 
indications of internal processes near the hinge of the depressed valve; like 
all the other Brachiopoda, the texture is granose within, with the external 
surface frequently spinose. The shell possesses a very singular peculiarity ; 
namely, that of its anterior margin being produced beyond that part occupied 
by the animal. 
The shells of this pretty numerous genus are known only in a fossil state, 
and are peculiar to the strata of the secondary formation, and which they in 
a great measure characterize; more especially the Carboniferous limestone ; 
they are also met with in the older Transition limestone, the Seatoschist of 
Snowden ; the Magnesian limestone of Breden, Derbyshire. 
I have adopted this generic name instead of Propvucta of Sowerby, as it is 
ingrammatical. 
Genus XI.— CYRTIA. — Dailman. 
Generic Character. — Shell longitudinal, inversely py- 
ramidal, inequivalve, subequilateral; one valve considerably 
depressed, the other convex ; hinge line rectilinear ; beaks 
in one valve only, and slightly incurved. 
Cyrtia cuspidata. Plate XI. fig. 11. 
Found in the Carboniferous Limestone, St Vineents Rock, near Bristol. 
This genus consists exclusively of fossil species. Our type of the genus is 
Spirifer cuspidatus of Sowerby. 
Genus XII.— ATRYPA. — Konig. 
Generic Character. — Shelt longitudinal, equivalve. 
equilateral ; hinge line slightly curved, umbones small, and 
not incurved. 
Atrypa reticularis. Plate XI, fig. 12. 
Genus XII].— TEREBRATULA. — Bruguiére. 
Generic Character. — Shell inequivalve, equilateral, 
