part 4] OF THE MIOCENE OF CEYLON. 593 



PlNNA PACHYOSTEAGA sp. UOV. (PL XXIX, figs. 3 & 4.) 



1836. P An Pinna nobilis Deshayes, in 'Expedition Scientifique tie Moree ' 

 vol. iii, p. 113. 



This species is represented only by a large fragment of the right 

 valve, with a portion of the edge of the associated left valve (the 

 holotype — Brit. Mus. L. 28743) and by three small fragments 

 (L. 28744). Nevertheless, it shows features so distinctive that a 

 new specific name appears justifiable. 



Shell deltoidal, with acuminate umbo (probably very similar in 

 outline to the recent Atrina nigra Chemnitz sp.). Dorsal and 

 antero-ventral margins diverging, in the part preserved, at an 

 angle of 65°, this angle becoming more acute towards the apex. 

 Antero-ventral and postero-dorsal sectors about equal, the former 

 marked only by growth-lines, the latter bearing six coarse costal, 

 increasing to seven by intercalation of an extra costa in the middle 

 of the sector, at a distance of. probably, about Go mm. from the 

 apex (with probable further increases beyond, one of the fragments 

 showing five cost* in a space of 42 mm.). Test prismatic, very 

 thick, especially towards the antero-ventral margin, varying from 

 1 to 9 mm. in the holotype, but attaining 14 ram. in one of the 

 smaller fragments (PI. XXIX, fig. 3). The cost* are solid 

 thickenings of the test, and do not show on the interior. 



I refer this species to the genus Pinna (although it is quite 

 likely that it may really be an Atrina), on the principle that, in a 

 case of uncertainty, it is better to use the more familiar designation. 



It is not mrpossible that the fragments of a very thick-shelled 

 Pinna, described by Deshayes from the same series of beds as 

 Ostrea virleti in Greece, belong to this species. The fragments 

 were evidently not good enough to be figured, and Deshayes only 

 referred them, with great doubt, to P. nohilis, because that was 

 the characteristic species of the adjacent seas. In the 2nd Mediter- 

 ranean stage of the Vienna Basin, however, Pinna hroccJu'i 

 A. d'Orbigny has a thickness of 2 - 5 to S mm. according to 

 Hoernes, and the Greek fragments may belong to that species. 



A g e. — Miocene ( Vindobon ian ) . 



Locality. — Minibagalkanda, Southern Province (Ceylon). 



Si'oxdvlus waylakdt sp. nov. (PI. XXIX, fig. 5, and text- 

 figs. 2-3, p. 594.) 



Inflated-lenticular, approaching globose: profile of valves pass- 

 ing from strongly convex to slightly concave near the margins. 

 Slightly inequivalve ; distinctly inequilateral. Height and length 

 approximately equal, thickness = 3/5 'of the other dimensions. 

 Maximum measurements— approximately 75 mm., 75 mm., 45 mm. 

 Height of the left valve=about 14/15 that of the right valve. 

 Horizontal distance of umbo from the anterior end=about 9/10 of 

 its distance from the posterior end. 



Ears distinct ; cardinal area very small, and difficult to expose. 



