154 BRITISH PALAEOZOIC SPONGES. 



36. Pachastrella humilis, Hinde. Plate IV, fig. 7. 



1880. Qtjadeieadiate spicule, Carter. Ann. and Mag. Nat. Hist., ser. 5, vol. vi, 



p. 212, pi. xiv, fig. 17. 



This name is proposed for detached four-rayed spicules of the normal type- 

 The rays are simple, three of them are subequal in the same spicule, whilst the 

 fourth or vertical ray is apparently shorter than the others. The rays are about 

 '3 mm. in length by '07 mm. in thickness. These are more regular in form 

 besides being distinctly smaller than those placed under P. vetusta, and they appear 

 to indicate a distinct species. They are of rare occurrence in the decayed chert 

 of Ben Bulben, and specimens in a fragmentary condition are present in the 

 Sponge-beds at Halkin. In both these localities they are siliceous, and in the 

 same mineral condition as the hexactinellid spicules intermingled with them. 



Distribution. — Upper Limestones : Ben Bulben, Sligo (J. Wright). Yoredale 

 Series : Henblas, Flintshire. 



Sub-Order. — Lithistid^e. 

 Family. — Rhizomorina. 

 -Cnbmidiastrum, Zittel. 



1878. Studien fiber fossile Spongien. Zweite Abth. Abhandl. d. k. bayer. Akademie 

 der Wissenschaften, CI. ii, Bd. xiii, Abth. 1, p. 109. 



Syn. — Cnemidium (in part); Achilleum (in part), Goldfuss, Quenstedt; Cnemi- 

 spongia, Quenstedt ; Cupulospongia (in part), D'Orbigny ; Cnemiopelta, Cnemi- 

 psechia, Pachypsechia, ? Oeriopelta, Trachycinclis, Pomel. 



Generic Characters. — Sponges for the most part simple, rarely compound, 

 conical, cylindrical, turbinate, and vasiform, with thick walls and deep cloacal 

 cavity. The walls are traversed by numerous vertical fissures, which towards the 

 exterior bifurcate and anastomose with each other. These fissures consist of 

 canals placed directly over one another and separated from each other by thin 

 partitions of the spicular skeleton. A smooth dermal layer extends over both the 

 outer and inner surface of the Sponge-wall, and the canal-apertures either project 

 slightly above this layer or are in shallow depressions below it. The skeleton 

 consists of moderately large spicules of curved irregular forms, branching at the 



