200 SYNOPSIS OF THE CHARACTERS OF THE 



This beautiful species is not likely to be confounded with any other of the genus ; the specimens are often 

 of considerable size, two inches being the usual length. 



' Ptylopoea. Sc. MSS. 



Gen. Ch. — Flabelliform, or infundibuliform, attached by roots, from which a strong midrib arises, giving 

 origin on each side to thin, equidistant interstices, connected by regular dissepiments ; external face of the 

 interstices carinate, and bearing two rows of pores. 



Ptylopora FLUSTRIFORMIS. Pllil. SP. 

 Ketepora flustriformis. Phil. Geol. York., and Phil. Pal. Fos. 



Sp. Ch. — Midrib square, coarsely striated ; interstices thick, equidistant ; feuestrules small, oval, equal ; 

 dissepiments as thick as the interstices, equidistant; pores small, round, five or six to the length of a fenestrule. 

 A very beautiful, feather-like coral. 



' Ptylopora pluma. Sc. MSS. (PI. XXVIII. fig. 6). 



Sj). Ch. — Midrib very thick; general form feather-shaped; interstices with a regularly poriferous keel; 

 pores small, rovuid, four to the length of an interstice. 



The coral to which Dr. Scouler has given this name ajDpears to differ from the P. flustriformis, in its nar- 

 row, feather-like outline, the length being three times the width ; the midrib is also larger and more distinctly 

 poriferous. I have not, however, examined good specimens. 



Fenestella. Miller. 



Gen. Ch. — Cup-shaped, conical, reticulated, formed of thin, carinated, radiating ribs (interstices), con- 

 nected by transverse, nonporiferous bars (dissepiments), two rows of prominent pores on the external, carinated 

 fiice of each interstice. 



This excellent genus is easily distinguished from Retepora by its nonporiferous, transverse bars, and its 

 poriferous face being external instead of internal, as in that genus. From my genus Polyjwra it is distin- 

 guished by its poriferous face being carinated, and having normally but two rows of pores (in most Fenes- 

 tella I have observed a very irregular row of small pores on the central keel) ; from Hemitrypa it is known 

 by the apparent want of the external (imperforate ?) sheath, which at present seems pecidiar to that genus*. 



Fenestella antiqua. Lons. 



Fenestella antiqua. Lons. Geol. Trans, (not Sil. Syst.) — Fenestella antiqua. Phil. Pal. Fos. 



Sp. Ch. — Interstices thin, equidistant, irregularly branching ; dissepiments very thin, equidistant; fenes- 

 trules nearly twice as long as wide, slightly rounded ; pores large, prominent, five to the length of a fenestrule, 

 the two rows apparently inosculating. 



This species differs from the true F. antiqua of the Silurian rocks, as Mr. Lonsdale and Professor Phillips 

 have already noticed, in the contiguity of the two lines of pores. 



Fenestella carinata. MCoy. (PL XXVIII. fig. 12). 



Sp. Ch. — Interstices externally, close together, irregularly bifurcate; dissepiments and interstices flattened, 

 of eqtial breadth, and on the same level; fenestrules circular ; jwriferous face of interstices angular, with a strong, 

 longitudinal keel in the middle ; dissepiments very thin, small, rounded ; fenestrules elongate, oval. Two irre- 

 gular rows of pores with projecting margins, and one irregular row on the central keel. 



" I have recently observed this sheath in some of the true FenesteUa ; Hemitrypa is, therefore, possibly only the 

 perfect state of Fenestella. 



