202 SYNOPSIS OF THE CHARACTERS OF THE 



their own diameter apart, placed much on the sides, so as to indent the margins of the fenestrules deeply ; 

 they are placed alternately, usiially two to each fenestrule, and one at the origin of each dissepiment ; about 

 five interstices in the space of one line ; reverse with coarse, waving striffi. 



This beautiful little species in its mode of growth resembles a little shrub, or tree, having a short, thick 

 trunk, and suddenly expanding to a nearly circular head ; it is not uncommon ; the specimens being about 

 one-fourth of an inch long, and very constant in form. 



Fenestella hemispherica. M'Coy. (PI. XXIX. fig. 4). 



Sp. Ch. — Hemispherical, cup-shaped ; interstices and dissepiments exceedingly minute ; interstices thin, 

 sharply carinated, reverse longitudinally striated ; dissepiments one-fourth the thickness of the interstices ; 

 fenestrules rectangular, wider than the interstices, and somewhat longer than wide ; pores small, twice their 

 diameter apart, with raised margins which do not indent the edge ; about three pores to the length of a fenes- 

 trule. 



This beautiful coral forms a hemispherical cup, the root or base being slightly excentric, a few longitudinal 

 folds or undulations disturb the regularity of the form; the substance of the coral itself is so exceedingly deli- 

 cate, that it is only after a close examination with good lenses that it can be at all made out ; the fenestrules 

 are usually longer, and the pores consequently farther apart than in the drawing. Length one inch two lines, 

 diameter one inch six lines ; there are about seven interstices in one line. 



Fenestella laxa. Phil. 



Retepora laxa. Phil. Geol. York. — Fenestella laxa. Phil. Pal. Fos. 



Sp. Ch. — Interstices thick, rounded, very irregularly branched, dissepiments round, nearly equal to the 

 interstices in thickness ; fenestrules very large and extremely irregular in size and shape ; there is no keel on 

 the poriferous face of the interstice ; pores numerous, small, approximate, with raised margin, reverse regularly 

 granulated in quincunx. 



This species is distinguished by its great size, the looseness and irregularity of its branching, and its regu- 

 larly granulated reverse. The interstices are half a line in thickness. 



Fenestella membeanacea. Phil. sp. 



Ketepora membranacea. Phil. Geol. York. 



Sp. Ch. — Elongate, conical; interstices straight, equidistant, with a sharp, central keel; dissepiments 

 nearly equal in thickness to the interstices ; fenestrules elongate, rather wider than the interstices, nearly three 

 times as long as wide ; pores small, about three in the length of a fenestrule ; nonporiferous face granulated. 



This abundant species is remarkable for its very elongate, conical shape ; it is fixed at the base by long, solid, 

 nonj)oriferous roots, of considerable thickness ; the lengthened form of the regular fenestrule, and the granula- 

 tion of the nonporiferous face, are the most important specific characters. This species often grows to a length 

 of nine or ten inches ; five interstices occupy about one line. I have recently seen a specimen exhibiting traces 

 of the external sheath of Hemitnjpa. 



Fenestella MoRrasn. M'Coy. (PL XXVIII. fig. 14). 

 Sp. C/(.— Expanded, conical, cup-shaped ; interstices thick, round, regularly branching ; dissepiments very 

 thin, at nearly equal distances ; pores large, nearly their own diameter apart, with very prominent margins ; about 

 six to the length of a fenestrule ; fenestrules slightly irregular, usually quadrangular, one-third longer than wide, 

 reverse nearly smooth. 



