1863.] DtTJfCAN — WEST INDIAN COSAtS. 413 



whilst in some there are three cycles in some systems, and only two 

 in others, the corallum being large. 



The form which I consider typical of the species has four perfect 

 cycles in six systems ; but in some corallites the rudimentary sixth 

 and seventh orders of a fifth cycle exist. The specific character- 

 istics — the thick and great development of the septal laminae at their 

 wall-end, and the more or less linear, but entire, condition of their 

 internal parts — are seen in all these forms, in the primary, secondary, 

 and tertiary septa, according to the relative septal arrangements. 

 In some corallites with a low septal number, the primary septa alone 

 are thus characterized ; and as the higher cycles are seen, so the 

 secondary and tertiary septa become enlarged and resemble the 

 primary. The septa of the higher orders are either linear through- 

 out or slightly enlarged at the wall ; and as they approach the tertiary 

 or quaternary, as the case may be, they are seen to become more 

 equal to them in size. In examining these forms allowance must 

 be made for their fossil condition ; and attention must be given, in 

 examining transverse sections of corallites, that they are quite at 

 right angles to the corallite, for any obliquity will, of course, dimi- 

 nish the peculiar spear-shape or mace-shape of the septa, and render 

 them more like a paddle, or a leaf with the stalk attached. 



The tendency of the higher orders of septa to become linear 

 throughout, or to be less decidedly large at one end and thin else- 

 where — that is, more or less uniformly thick, but in a less degree 

 than is usual at the wall, — is seen throughout the species ; and in 

 a gigantic variety, where the fully developed corallites have twelve 

 or fourteen septa in every system, the whole of the septa are less 

 decidedly thick at the wall, and are either more or less so throughout, 

 or present the usual form of the septa in a modified degree. 



This species is found throughout the great Marl-formation, and 

 presents every variety of siliceous fossilization, from that character- 

 ized by silicification of the sclerenchyma and infiltration of the inter- 

 spaces by granular carbonate of lime, to that where all is siliceous and 

 capable of polish. Destructive silicification almost invariably exists 

 in a greater or less degree ; and as the sections preserved were made, 

 as a rule, for ornament or amusement, I have seldom seen accu- 

 rately transverse and longitudinal views of the corallites. 



All the specimens, with the specific peculiarities mentioned, may be 

 ranged in seven groups : that which contains the detailed characters in 

 their greatest intensity, generally, may be considered the typical form. 



a. Aste^a crassoiamellata, typical form. PI. XIII. figs. 1 a-1 c. 

 Corallum large, irregularly convex above. Corallites tall, large, 

 crowded here and there, but not so much so higher up or at the sur- 

 face. Calices circular, but more or less elliptical when on an irre- 

 gularity of the surface ; very large, and separated from each other by 

 well-marked, furrow-shaped, polygonal tracts ; tracts marked by 

 costal elevations and by granules*. Calices crateriform, not much 



* As none of the specimens exhibit perfect calices, many of these characters 

 have, of necessity, been taken from casts. 



