ORDER I CALCISPONGIAE PII A II MT1K >.\ Ms 



seen radiating in all diivrt ion> tn.m miim-roii- rent ivs .t rry>talli.-at inn. SI.HH- 

 times such calcareous skeleton- afterwards Keeomr silicilicd. It i- 

 therefore, that the present eheniieal n>mpijt in \ a I'M il -[lon^e fnrni.-li- n~ 



Fibres of a PAorctroTM. composed 



raynl f.iiiciiI.'S (r,-ri<i<MI<i oyUndliOO, 

 sp. Upper Jurassic), *>/i. 





Fi... 88. 



--il <-al<"il<-<,ii- 



spi.n^i- alt'-M-d liy crystalli.sa. 

 tiun, 4" ,. 



no clue in regard to its original character, since during the process of fossilisatimi 

 a silicious skeleton may become converted into a calcareous, and u ealeare<>n> 

 into a silicious. 



Of the four orders of calcareous sponges Pharetrones, Si/cones, A scone*, and 

 Is-ii'-mics only the first two are of practical importance to the palaeontologist, 

 traces of the others being either wanting or extremely fragmentary. 



Order 1. PHARETRONES. Zittel. 



Wall thick ; canal-system like that of the Lithistida, though sometimes indi*tii1 

 and apparently absent. Spicules arranged in solid anastomosing fibres ; a smooth or 

 corrugated dermal layer frequently present. Devonian to Cretaceous; unknown in 

 Tertiary and Recent. 



Eudea, Lamx. Cylindrical or club-shaped, usually simple, rarely branching. 

 narrow, tubiform, extending to the base, and terminating above in a 



Fio. 89. 



Peronidella 



'. Must. 



sp. Upprr )"!- 

 as>ic- ; Mu^gcii- 

 dorf. Reduced V-'- 



Fio. 00. 



Peronidella dumosa, From. 

 s|i. mis; Berklingen, Brattn- 

 schweig. Natural size. 



Fin. HI. 



\CorynellaQuenstedti, Zitt. Conil-Ha- : Natt- 

 li.'iin. o, Six>nge, natural size ; ', 

 fibres, 4 /i. 



round osculum. Dermal layer smooth, perforated by ostia of short canals. 

 Triassic and Jurassic. E. clavata, Lamx. 



Peronidella, Zitt. (antea Peronella, Zitt. non Gray, Sip/wiwcoelw, Pol,' 



