85 
6. Spieifer nudus, Soiverhy. 
Spirifera nuda, Sowerby, 1840, Trans. Geol. Soc. London, V (2), pi. 57, fig. 8. 
„ pulchella, Idem, 1840, ibid., pi. 57, fig. 9. 
,, nuda, J. Plnllips, 1841, Pal. Foss. Cornwall, p. 78, pi. 31, fig. 138. 
Spirifeu nudus, Ford. Eoemer, 1855, Bunker’s Palajontograpbica, V, pi. 4, fig. 20. 
Spirifera nuda, T. Davidson, 18G5, Mon. Brit. Dev. Brach., p. 38, pi. 4, fig. 17-22. 
Shell small, sub-oval, a little broader than long, greatest width about 
the middle of its length. Ventral valve convex, deeper than the opposite 
one ; beak small, incurved, rather prominent. Area a very pronounced 
triangular shape, with the fissure partly closed by a pseudo-deltidium ; sinus 
rather deep and relatively broad, rising at the apex of the beak ; one or two 
strong ribs are on each side of the sinus. The dorsal valve is less convex 
than the ventral, and is provided with a rather prominent fold and one or two 
lateral ribs, corresponding to those that have just been mentioned. 
Dimensions. — Length, five millimetres ; width, six and a half milli- 
metres ; thickness, three millimetres. 
Observation . — The preceding description and dimensions are quite 
applicable to the only specimen of the species I have before me ; but Mr. 
Davidson rightly remarks that this species is very variable as regards the 
extent of its area, and the number of lateral ribs with which the surface is 
provided, and which may be altogether wanting in some specimens. 
Horizon and Localities .— was the first to record the occur- 
rence of this species in the Middle Devonian limestone of Dockyard, near 
Plymouth. After him, it was discovered in several other localities in 
Devonshire. Mr. Clarke has collected it in a black limestone containimr 
Atrypa plicatella, L. G. de Koninck, in the Yass District. 
Division — SC A. 
LAMELLIBRANCHIATA. 
PARACYCLAS, J. Hall. 
Although it is rather difiicult to define this genus satisfactorily, in 
consequence of the impossibility of procuring the perfect hinges of the shells 
upon which it has been founded, I have no doubt that one may succeed in 
