CARBONIFEROUS FOSSILS OF IRELAND. 7 



Orthoceras cmcTUM. Soiv. (not oi Phil.) 



Orthoceras cinctum; Sow. Min. Cou. 



Sp. Ch. — Shell very gradually tapering, section circular ; siphuncle central ; septa simple, distant; smface 

 with fine, close, sharp, transverse stria3. 



A few cylindrical fragments of this species have occurred. 



Orthoceras cylindraceum. Flem. (Not of Sow.) 



Ortliocera cylindracea. Flem. An. Pliil. 



Sp. Ch. — Very gradually tapering, septa slightly waved, numerous; one and a-half lines apart; siphuncle 

 very small, central. 



This species is not nearly so cylindrical as some others, a specimen four inches in length, tapering about 

 four lines. The O. inequiseptum (Phil.) is very closely allied to this species, but has the septa closer together. 

 The O. cylindraceum of Sowerby is quite distinct, and should have the specific name changed. 



Orthoceras filiferum. Pliil. 



Orthoceras filiferum. Phil. Geol. York. 



Ch. Sp. — Very gradually tapering ; siphuncle central ; septa simple ; surface with simple transverse striaj 

 or ridges. 



The specimens I have referred to this species have the annular ridges larger and more obtuse than in the 

 O. cinctum. 



Orthoceras mucronatum. M'Coy. (PI. I. fig. 1.) 



Sp. Ch. — Shell rapidly tapering, smooth; tip mucronate ; section oval; siphimcle slightly excentrlc. 



This very curious Orthoceras reminds us by its form of the Belemnites mucronatus of the chalk. The 

 mucronate tip is a character I have not observed in any other Orthoceras'^. Tapers more rapidly than O. ovale. 

 Length of specimen two inches ; breadth at base six lines, tapers three lines. 



Orthoceras ovale. Pliil. 



Orthoceras ovale. Phil. Geol. York. 



Sp. Ch. — Shell very gradually tapering; section broad oval, septa simple; siphuncle nearly central. 

 This abundant species tapers very slowly ; a specimen three inches long and nine lines in diameter at the 

 base, diminishes three lines ; the septa are one and a half lines apart ; surface smooth. 



Orthoceras pyeamidale. Flem. 



Orthooera pyramidalis. Flem. An. Phil. 



Sp. Ch. — Shell rapidly tapering ; septa slightly waved, distant ; siphuncle small, central. 



This species tapers rather rapidly, a specimen, four and a half inches long, measuring an inch in diameter 



" Captain Portlock has figured some mucronate species since the above was written. See Geol. Report, &c. 



