Mr. H. J. Carter on known Fossil (Sponges. 283 



hina (Zeitsclirift f. wiss. Zool. 1880, Bd. xxxiv. Taf. xx.- 

 xxii.). 



Next come tlie Ceratina (Order II.), wliich, with the 

 exception of the following order, viz. Psammonemata, appear 

 to be bj far the most abundant of all existing sponges, and at 

 the same time may reach a very large size [ex. gr. the Luf- 

 faria from the West-Indian seas, in the British Museum), 

 whose kerataceous fibie is so thick and hard when dry that it 

 breaks with the shining fracture of hard glue. 



This horn-like substance, which, as before stated, has lately 

 received the name of " spongin," is in its elementary compo- 

 sition so nearly allied to the chitin of the insect-skeleton that 

 it seems strange that the latter should be handed down in a 

 fossilized state (if such should be the case) and not the former. 



According to Krukenberg the elementary composition of 

 spongin and chitin respectively is as follows : — 



Spoiigiu 0.30 11.46 N. 9 0.13 



Chitiu 15 26 2 10 



Thus (to me) the former is the densest and physically the 

 most solid of the two, especially in Luffaria. 



What the branched forms in the Quadersandstein of 

 Saxony, called by their discoverer Geinitz " Spongites saxoni- 

 cus,^^ or the net-like figuration on the surface of crooked 

 cylindrical bodies (" Rhizocorallium,^'' alluded to by Zittel, 

 ' Handbuch der Palaiontologie,' pp. 142, 143), may be remains 

 to be decided. 



Again, there is no mention of the PsAMMONEMATA (Order III.) 

 in a fossilized state, although I found them in a recent one in 

 such great abundance in the " ridge " on the south-east coast 

 of Arabia above alluded to — seeming to indicate in this in- 

 stance the first step towards fossilization, if not also what 

 would probably have taken place and been recognized in 

 former fossilizations if such had occurred. 



My Dysidia antiqua from the Carboniferous of Ayrshire 

 ('Annals,' 1878, vol. i. p. 139) has been relegated by Dr. 

 Hinde to those kinds of sponges which come under my order 

 HoLORHAPiiiDOTA, by the generic name of '■'• llapUston " (Mon. 

 Brit. Spong. Palteontographical Society's vol. for 1887, pt. ii. 

 p. 147, pt. 1. pi. V. figs. 2, 2 a). 



Of the liiiAPHiDONEMATA, whose fibre is again corneous, 

 1 found a small branched fragment, apparently of a Ckalina^ 

 having the usual form of acerate spicule presented by that 

 family, in a detrital piece of chert from the remains of the 

 Upper Greensand so abundant in this locality (Budleigh 



