414 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 6, 



elevated above the surface. Wall thin, and rendered insignificant by 

 the great development of the septa at the margin. Fossa not deep. 

 Costae numerous, and, considering the diameter of the septa at the 

 wall, very small ; they project but little, and are, as a rule, alter- 

 nately large and small, not dentate, and often incline one to the other 

 at their free edge. The larger costse present regular enlargements 



Analysis of the Species. 



Intercalicular 

 furrow. 



a. Astrasa crassolamellata (type).j well marked 

 , var. mametica 



b. 



c. , var. pufchella . . . 



d. ■ , var. nobilis 



e. , var. minor 



/. 



-, var. Nugenti 



well marked 



less 



>■ well ■< 



marked 



less marked 



g, , var. magnifica ... well marked 



Septa. 



very 

 thick < 

 at wall 



very large at 

 wall 

 very f 

 thick \ 

 at wall [ 

 less thick 

 and more 

 linear 



Cycles. 



4, in some 5 



4 



variable 



variable 



2 and 3 

 4-6 



Diameter of 

 corallites. 



f-| inch 



inch 



3~2 



inch 



variable 



small, va- 

 riable 



■^ inch 



1 inch and 



more 



where the cross-tissue (dissepiments) of the exotheca joins them : 

 when there are more than four cycles of septa, the smaller costaa 

 are irregular as regards their appearance and development. Colu- 

 mella large, of lax laminae, parietal ; it does not project much at the 

 bottom of the fossa, and occupies a large space in the corallite. Septa 

 numerous, generally characterized by great enlargement at the wall, 

 and linear appearance in the rest of their course, the higher orders 

 being nearly linear at the wall also. The number of cycles varies 

 with the stage of development of the corallite. 



In young corallites there are six systems of three cycles. As 

 growth proceeds, the other orders of the fourth and sometimes of 

 the fifth cycle are gradually added. Some systems are defective in 

 certain orders, while others possess them. The largest corallites 

 have four perfect cycles, and a fifth in two or three systems ; the 

 ninth order being usually wanting. It is difficult, in the larger 

 corallites, to distinguish the systems on account of the resemblance 

 of the primary, secondary, and tertiary septa to each other. 



The primary septa are very thick externally, but delicate and linear 

 elsewhere; the linear part joins the rest suddenly, like the staff of a 

 big-headed spear ; at the junction the thick corners of the enlarge- 

 ment give off a lateral spine, like a piece of endotheca ; near the 

 costal end of the septa there are delicate lateral spines. The space 

 between the sets of lateral spines is more or less square. The 

 secondary septa are very like the primary. 



When there are more orders in the system than five, that is, when 

 there are six, seven, eight, and nine, the tertiary septa equal the pri- 

 mary and secondary, the blunt end terminating in the linear portion 

 a little nearer the wall. When there are four cycles, the tertiary 



