74 
Greville^ on New Diatoms. 
scarcely know what is tlie true form of the processes^ as in 
half the specimens I have seen they are not truly circular, 
but tending to broadly oval. 
AULISCUS. 
Auliscus nebulosas, n. sp., Grev. — Valve circular (with 4 
processes) ; no definite umbilicus ; radiating lines all uniform, 
extremely fine; minute puncta, forming irregular clusters 
beneath and between the processes. Diameter '0030''. (Fig. 
21.) 
Hab. Barbadoes deposit, from Cambridge estate; C. John- 
son, Esq., G. M. Browne, Esq. ; very rare. 
Of this beautiful species various examples have occurred 
to Mr. Johnson, Mr. Ralfs, and myself, but always with the 
surface so abraded as to prevent description. Perfect speci- 
mens have, however, been recently discovered. Nearly all 
the frustules which have been seen present the singular 
appearance of eight processes, the four of the subjacent valve 
alternating with those of the upper, and being almost equally 
conspicuous. In my figure I have represented the four 
belonging to the upper valve, in order to prevent confusion in 
the engraving. As all the discs hitherto observed possess 
this number, it is probably the normal one. The species 
belongs to the group characterised by very fine and crowded 
radiating lines ; but in the clusters of minute puncta, in the 
neighbourhood of the processes, it is also allied to A. racemo- 
sus. It wants, however, the circle of marginal puncta. The 
processes are circular, and large for the size of the disc. 
Auliscus parvulus, n. sp., Grev. — Very small ; valve circu- 
lar, with 4 processes ; structure obscure. Diameter -0015''. 
(Fig. 32.) 
Hab. Barbadoes deposit, from Cambridge estate, in slides, 
communicated by C. Johnson, Esq. 
I have been unable to make out any striation in the speci- 
mens of this species which I have examined. It apparently 
belongs to the same group as A. elaboratus and Johnsonianus , 
having the same pale, semi-opaque, somewhat dense appear- 
ance. I cannot refer it to any described species ; and, in- 
deed, it is so many degrees smaller than any one hitherto dis- 
covered, that there is good reason to regard it as distinct. It 
presents another example of valves with four processes. 
Auliscus ambiguus, n. sp., Grev. — Valve broadly oval, the 
whole surface filled up with a minute cellulation (no trace of 
converging or radiating lines) ; cellules 11 or 12 in -001". 
Longest diameter -0023". (Fig. 23.) 
