OF SOUTIIEEX INDIA. 
11 
that the very small foramen is hardly visible in the jicrfect shell ; the deltidium is 
small, tubercular in front, and apparently extends all round the foramen ; the 
umhonal ridges are slightly marked, short, curved, meeting at an angle of about 
95° ; they enclose a short smooth area on either side of the uinho, sliglitly encroach- 
ing vith its margin on the ha)mal valve. 
Localihj. — S. E. of Arrialoor; only a few specimens have been found in a 
wliitish sandstone. 
Form atio n. — Arrialoor group . 
This species appears to be the eastern representative of Bhijn. Ilantellana, from 
the more inflated varieties of which it differs by a well developed frontal sinus, and 
by having the radiating ribs somewhat more numerous and generally closer together; 
the beak also is considerably more incurved. Almost the sanie (hfferenccs arc appli- 
cable in a comparison with Rhyn. venlriplanata, which Schlocnhach separated from 
the last mentioned species (comp. Sitzungsb. Akad., IVicn, Math. Nat. Klasse, LVII, 
p. 215, pi. 3, figs. 8-10). 
3. Fuiyxciioxellx compressa, (Lam.) PI. I, Eig. 7. 
1819. Tcrehratida compressa, Lam., An. s. Tcrt., vol. vi, p. 2.5(5. 
1817. BhynclioncUa compressa, D'Orb., Pal. Fran^. terr. cret., vol. iv, p. 35, pi. 497, figs. 1 — 0, (non eadem 
apud Davidson, Diit. Cret. Draoh., p. 80.) 
Rhyn. tesla transverse elonyate snh-ovata, valva hccmall altera mullo convexiore, 
ad nmhoneni maxhne elevata, ambabiis maryincs versus valde depressis ; superficie 
rad'iathn 20-2G costata ; costis crassiuscnlis, suh-lceviyatis, svepisshne simplicibus, rare 
dichotomis ; fronte prof unde insinuata ; sinu 7-10 — costato, circiter tertiam partem 
latitudinis teslcc (equante ac planitiem valvidai hcemalis fere attinyente ; umbone 
valvce nenralis depresses modice projlelente, subrecto ; deltidio pjarvo, foramen omnhio 
circumdante. 
In identifying an Indian specimen with the European species, I adopt Dr. 
Schlocnbach’s views regarding the distinction of the original Rhyn. compressa of 
Lamarck and of D’Orbigny, and that named Rhyn. dlmidiala* by Sowerby, 
and recorded by Davidson in his Drit. Cret. Brachio])oda under the former name. 
In Rhyn. compressa the neural valve is very flattened and the hannal most conmx 
near the apex, but both valves are considerably flattened towards the margins, the 
sinus ecpials in Avidth about one-third the breadth of the shell, and is shallov'er or 
deeper, but scarcely reaching the Icwel of the coiwexity of the hannal vah'e ; the 
beak of the neural A'alvc is straighter than in d/m/diata, and the umhonal ridges less 
developed; the radiating ribs arc mostly simple, A'ery rarely bipartite, and, there- 
fore, considerably stronger at the periphery than in the middle of the shell ; the 
shell is very thick, and cast specimens appear to he, therefore, much less distinctly 
ribbed than covdd he presumed from the original surface. The geological position 
* With which Sehloenbach also identifies li. laiissima, and part of R. depressa of Davidson; Geogn. Palaeont. 
Beitrmge, by Benecke, 1808, vol. I, p. 486, and seq. 
