112 PALAEONTOLOGY OF NEW-YORK. 
Fig. 1 Jc. An enlarged portion of the margin of the cup, showing that the dentate process be¬ 
tween the rays appears externally, and extends downwards equally with the full ray. 
The number of rays usually seen in the cup (except when the dentate process in the 
margin is visible), is only half the number which will be counted in the outer cir¬ 
cumference of the cup. 
In cases where few and imperfect specimens only are accessible, it is important to bear in 
mind this circumstance, since in this species the rays can be so readily counted on 
the exterior surface. 
Position and locality. In the shale of this group at Lockport, Rochester, Marshall’s mill, 
Wolcott, and almost every other locality where the shale is exposed. ( state Collection.) 
Genus POLYDILASMA ( nov. gen.). 
[Gr. tfoXuj, multus, 6ig, duplex, and sXatfp.a, lamella ; in allusion to the numerous double lamellas.] 
Corallum turbinate; lamellae numerous, thin, apparently rising in pairs, and one often much 
stronger than the other ; cell broad, margin thick and strong, with a deep central pit; half the 
lamellae reaching to the centre of the cell, where they are complicated or contorted ; transverse 
septa in the centre below the base of the central part of the cup, obsolete or irregular. 
This coral is allied to Calophyllum, but does not show the transverse septa characteristic of 
that genus. The cell is very peculiar in its character, one half only of the rays extending into 
the deeper portion, giving it a peculiar aspect which is preserved in solid crystalline specimens, 
even when no rays are visible or when they are very indistinct. 
506. 1. POLYDILASMA TURBINATUM. 
Pl. XXXII. Fig. 2 a - h. 
Turbinate or clavato-turbinate, usually short; outer surface nearly smooth, or transversely 
somewhat rugose ; cell deep, gradually descending from the margin halfway to the centre, and 
then deepening almost vertically ; rays numerous, thin, becoming complicated before reaching 
the centre, often apparently crenulate on the weathered exterior ; transverse septa irregular, and 
sometimes nearly or quite obsolete. 
This species is of variable form, though usually short, turbinate, and rapidly expanding. The 
cup presents a peculiar feature of being suddenly depressed about halfway from the outer mar¬ 
gin to the centre; and this is likewise accompanied by the termination of one half of the rays 
at the same point, so that only half the rays of the margin reach the centre. The rays are also 
variously curved, complicated, or coalescing before reaching the centre. There is no evidence 
of transverse dissepiments in the cup, and indeed the great depth of the cell in the centre 
almost precludes their existence in many specimens. The worn exterior surface shows the 
lamellae in pairs; and these, on ascending, become again regularly duplicated, so that the 
increase of size is pretty uniform on all sides, and the corallum is usually nearly straight. The 
