204 SYNOPSIS OF THE CHARACTERS OF THE 



tematic zoologist ; in its thick, vmcarinated interstices, and small impressed pores, it makes an approach to the 

 genus Polypora, M'Coy, but they are disposed in two rows only, as in the true Fenestella. 



■ Fenestella quadeadecimalis. M'Coy. (PL XXVIII. fig. 13). 



Sp. Cli. — Interstices slightly flexuous, thin, irregularly branching; dissepiments thin, distant; fenestrules 

 very large, irregular in shape, pores very numerous, prominent, about fourteen to the length of a fenestrule ; 

 reverse finely striated longitudinally. 



This species is remarkable for the immense number of pores between one dissepiment and the next, four- 

 teen beino- the usual number ; the interstices are very thin, but often dilated at the point of branching ; the 

 fenestrules are of great size but very irregular. 



■ Fenestella tenulfila. Phil. sp. 



Eetepora tenulfila. Phil. Geol. York. 



Sp. CIt. — Slightly spreading, irregularly branched, interstices very thin, sharply carinated ; fenestrules 

 nearly square, little longer than wide ; width equal to twice the thickness of the interstices ; dissepiments half 

 the thickness of the interstices ; pores small, their prominent margins indenting the edge about three to the 

 length of each fenestrule ; reverse with waving, longitudinal striae. 



This delicate species is remarkable for the excessive thinness of the dissepiments and interstices, except at 

 the branchings ; the fenestrules are nearly square. There are about five interstices in one line. 



Fenestella undulata. Phil. sp. 



Eetepora undulata. Phil. Geol. York. 



Sp. C/j.— Interstices and dissepiments very thin; fenestrules large, irregular; pores very large; rather dis- 

 tant, prominent, indenting the margin, about four to the length of a fenestrule ; reverse with undulating, longi- 

 tudinal striaa. 



This is a loosely branched but very delicate species, the substance of the coral itself being very slender ; the 

 fenestrules are four or five times the width of the interstices ; the pores are only subalternate, and so large as to 

 give a nodular aspect to the interstices. It grows to upwards of two inches in length ; there are about two 

 interstices in the space of one line. 



• Fenestella varicosa. M'Coy. (PL XXVIII. fig. 8). 



Sp. Ch. — Interstices unequal, those from which the branches originate being twice the thickness of the 

 others ; dissepiments thin, irregularly placed ; fenestrules slightly irregular, usually quadrangular ; pores mode- 

 rate, unequal, from four to six to the length of a fenestrule ; reverse nearly smooth. 



This is one of the most extraordinary species with which I am acquainted, from the character of some 

 of the interstices s\iddenly increasing to double their normal thickness, and, after giving out numerous tliin 

 branches, chiefly from one side, dwindling again to the original size, and continuing their course. Whenever, 

 from the origin of the interstices, it becomes necessary for one of those thin branches to dichotomize, it suddenly 

 doubles Its thickness for a certain length, and, as long as it remains thick, It gives off branches as before ; all the 

 interstices are slightly flexuous ; the reverse Is very convex, and nearly smooth. 



• Hemitrypa. Phil. 



Gen. Ch. — Poljrpldom, a stony, cup-shaped net-work, keeled, and poriferous, as In Fenestella, covered 

 with an external (imperforate ?) sheath. 



