288 Prof. F. M'Coy on some new genera 



The sulcated appearance of the cast and the linear arrangement 

 of the cells easily distinguish this species from the Stictopora 

 [Ptiiodictyd) acuta (Hall, sp.) By grinding down a fragment I 

 have ascertained with certainty the presence of the flat internal 

 axis, which is however of great delicacy, and not to be seen in 

 the shale or sandstone specimens. 



Not uncommon in the slates of Llansaintfraid ; calcareous 

 schists of Mathyrafal, and limestone of Girvan. 



Ptilodictya fucoides (M 'C oy ) . 



Sp. Char. Corallum forming very thin, flat, submembranous, 

 foliaceous, linear expansions, averaging li to 2 lines wide, 

 frequently dichotomizing at an acute angle, branches very 

 rarely, but occasionally anastomosing ; cells extremely small 

 (eight in the space of 1 line), about eighteen rows in the width 

 of the frond, very close quincuncially arranged, without per- 

 ceptible linear disposition ; internal axis smooth, nearly mem- 

 branous. 



The extreme minuteness, number and close disposition of the 

 cells easily distinguish this species fi'om the P. acuta or costulata, 

 and often give the specimens a resemblance to some fucoid. 



Not uncoumion in the schists of Llansaintfraid ; schists of 

 Gelli Grin, Bala ; and schists of Corwen. 



Fenestella patula (M'Coy). 



Sp. Char. Corallum forming small semicircular expansions about 

 half an inch in diameter ; interstices broad, strongly carinate, 

 slightly flexuous, and dichotomizing very frequently (usually 

 at rather less than every line in height), about seven in the 

 space of 2 lines; fenestrules about one-third wader than the 

 interstices, of very irregular shape, but nearly equal in length ; 

 dissepiments strong, about half a line apart ; pores large, very 

 prominent (about three to the length of an interstice) . 



This species is more nearly allied to the Retepora {Fenestella) 

 antiqua of Goldfuss, than the Silurian species referred to it by 

 Lonsdale {F. subantiqua, D'Orb.) ; from the latter species it is 

 easily distinguished by its thick, widely divaricating and fre- 

 quently branched interstices, the irregular shape of the fenes- 

 trules, and the much fewer and more prominent pores. 



Not uncommon in the Wenlock limestone of Dudley. 



Fenestella rigidula (M'Coy). 



Sp. Char. Corallum formed of very slender ridged straight in- 

 terstices, branching seldom (at distances of about every 10 

 lines), several interstices often branching at the same height, 



