Vol.51.] ME. R. B. NEWTOK ON FOSSILS FROM MADAGASCAR. 83 



towards the umbonal area ; anterior margin straight, with vertical 

 sides ; posterior area curved ; ornamented with numerous, closely- 

 set, concentric lines of growth. 



Dimensions. — Height = 44 mm.; length = 25 mm.; depth=10 mm. 



This specimen consists of a fragmentary right valve of a Mytilus, 

 with, unfortunately, its umbonal and hinge characters missing. The 

 shell-structure is well preserved, exhibiting most distinctly the fine 

 concentric striae. This, together with its almost straight anterior 

 margin and its generally depressed form, would suggest its being 

 a new species. It probably comes closest to Mytilus tigrensis of 

 W. T. Blanford 1 from the Antalo Limestones of Abyssinia, which has 

 its valves of a similar depth, but is decidedly more broadly convex, 

 having a curved anterior elevation and possessing less regular lines of 

 growth. 



Horizon. — From the Oolite (probably Lower), associated with 

 Steneosaurus Baroni. 



Loc. — Andranosamonta village. 



MODIOLA ANGTTSTISSIMA, Sp. UOV. (PI. III. fig. 4.) 



Shell elongate-oval, strongly arched ; anterior side deep, umbonal, 

 and rather concave : posterior side obliquely curved ; vertical 

 area narrow and acutely terminal ; ornamented with numerous 

 concentric imbricating stria?. 



Dimensions. — Height=33 mm. ; length= 15 mm. ; depth = 11 mm. 



This is represented by a right valve, with its shell-structure 

 beautifully preserved though somewhat fractured posteriorly. It is 

 a narrower and straighter form than Sowerby's Modiola imbricata, 

 with a more vertical anterior side. It is regarded as a new species 

 under the name of Modiola angustissima. The specimen was 

 obtained from the matrix enclosing the remains of Steneosauras 

 Baroni. 



Horizon. — Lower Oolite. 



Loc. — Andranosamonta village. 



Coebttla pecttnata, J. de C. Sowerby. (PI. III. figs. 17, 18.) 



Gorhula lyrata, J. de C. Sowerby, Trans. Geol. Soc. Loudon, ser. 2, 

 vol. v. pt. ii. (1840) p. 327, pi. xxi. fig. 13. 



Gorhula pectinata, J. de C. Sowerby, ibid. vol. v. pt. iii. (1840) 

 p. 718, pi. lxi. fig. 4. 



The characters of this Indian species are very marked and 

 definite. The shell is trigonal, subglobose, and of almost equal 

 height and length ; it has bold concentric and elevated ribs, 

 between which are closely-set transverse striae ; these striae are 

 more pronounced on the left valve and nearly obsolete on the other ; 

 the anterior end is deeply excavated, but without any circumscribed 

 lunule, while the posterior area exhibits a concave ligamental 



1 ' Observations on the Geology and Zoology of Abyssinia,' 1870, p. 201 & 

 pi viii. fig. 3. (Type in British Museum.) 



