OF SOUTHERN INDIA. 389 



ribbed; hinge edentulous ; muscular scar indistinct; type, M. salinaria, Schloth. 

 sp. Species of this genus are as yet only known from triassic rocks of the Alps, 

 Himalayas, New Zealand, and North America. 



9. Salohia, Bronn, 1830, (emend. Wissm.), (Jahrb. f. Min., &c., &c., i, 284). 

 Semi-circular or semi-oval, with a straight edentulous hinge line and almost central, 

 scarcely prominent, beaks ; valves rather compressed, equal, radiately ribbed, the 

 ribs placed close to the hinge line being usually conspicuously thicker than others ; 

 wings sub-equal, rounded at their terminations and not emarginated, muscular 

 scars indistinct ; type, S. Lommeli, Wissm. 



The original species described by Bronn is noted as S. salinarum, and is 

 based upon an imperfect specimen, apparently restored to a much oblique and 

 inequilateral form. It has the anterior wing conspicuously inflated along the 

 hinge margin and hollow internally. 



10. Fterinea, Goldf., 1832, (Petrsef. Germ., 1834, pi. ii, p. 133). Obliquely 

 oval, inequilateral, moderately tumid, with a long, straight hinge line, produced 

 anteriorly in a shorter, posteriorly in a longer wing, equivalve or sub -e qui valve, 

 anteriorly below the wing indented by a byssal opening ; hinge-area externally 

 striated, rather broad and thickened, apparently for the purpose of the attachment 

 of the ligament ; hinge internally with a few short oblique ribs and posteriorly 

 with a few longer ones, the latter originating below near the apex and extending 

 to the large posterior muscular scar ; anterior muscular scar small, deep, situated 

 at the base of the shorter wing close to the apex; type. Ft. Icevis, Goldfuss. 

 All the known species are palgeozoic, chiefly Devonian. The surface is either 

 smooth or radiately striated and ribbed. The hinge ribs are generally placed 

 in connection with the ligament, but from Goldfuss' and Sandberger's 

 figure of the type species, it seems tolerably clear that this explanation is not 

 supported by the internal structure of the valves (vide Sandberger's Schichten- 

 syst. von Nassau, &c., pi. xxx). Billings separated a silurian form under the name 

 of Bopteria (E. typicaj on account of a supposed external ligament and equal 

 valves, but these characters would alone not indicate a generic distinction from 

 'Fterinea. 



11. Fseudo-monotis, Beyrich, 1862, (Zeitsch. deutsch. Geol. Gesellschaft, 

 vol. xiv, p. 10. JEumicrotis, Meek, 1864, Am. Journ., Sc. and Arts, xxxvii, p. 218). 

 Sub-orbicular or roundly oval, the right valve being usually more or less convex, 

 with small, or nearly obsolete, wings and prominent incurved beaks ; the left is 

 conspicuously flattened or slightly concave, with barely prominent beaks and with a 

 straight, thickened hinge line, sometimes provided with a flattened tooth-like projec- 

 tion below and an oblique ligamental groove posterior to it, corresponding to a 

 similar groove or pit in the other valve ; the anterior end has below the beak a 

 narrow deep byssal incision and a small, sometimes almost obsolete, ear above it. 

 Posterior adductor muscle large, sub-central, anterior minute, at the base of the wing ; 

 surface usually covered with radiating ribs; type, Gryphites speluncaria, usually 

 referred to Monotis or Avicula; Fs. JSawni, Meek and Hayd., from the Permina 



