362 W. J. SOLLAS ON THE STKUCTURE AJfD 



27. On the Strfctuee and Aepinities of the Genus Peotospongia 

 {Salter). By W. J. Sollas, Esq., M.A., E.E.S.E., P.G.S., kc. 

 (Read May 12, 1880.) 



1. Liteeatuee. 



1861, Saltee, Q. J. G. S. vol. xx. p. 238, pi. xiii. ^^. 12 a, h, 

 1871, HiOKs, Q. J. G. S. vol. xxvii. p. 401, pi. xvi. figs. 14 to 20. 

 1877, ZiTTEL, Abh. der k. bayer. Akademie derWiss. 2. Cl., xiii. 

 ]3d. " Studien 11. fossile Spongiea " (p. 45 sep. copy). 



1877, Caetee, Ann. and Mag. Kat. Hist. Ser. 4, vol. xx. p. 177. 



2. HiSTOET. 



Saltee, who was the first to introduce this Sponge to our notice, 

 describes it as exhibiting a loosely reticulate skeleton, composed of 

 large cruciform spicules, the rays of which lie all in one plane and 

 cross each other at an angle of 80°. He adds that the only sponge 

 resembling it is his Amphispongia, which he regards as allied to 

 Grantia — a view quite in accordance with his ideas in general on the 

 Palseozoic sponges, most of which he seems to have referred to the 

 Calcispongia. In a foot-note he gives a quotation from a letter by 

 Dr. Bowerbank, who, in equal accordance with his general opinions 

 as to the affinities of fossil sponges, regarded Protospongia as allied 

 to the recent horny sponge Spongionella, Bwbk., its orginally horny 

 fi-bres having, according to him, been replaced by iron-pyrites. 



Hicks describes some spicular remains which he thinks may be- 

 long to Protosjyongia, and gives a diagrammatic figure of a fine 

 specimen which he had discovered of Salter's original species, P, 

 feiiestrata. 



Zittel places these Sponges with the Hexactinellidge, and in his 

 group Dictyonina, which is nearly equivalent to Carter's Vitreo-hexac- 

 tinellidee. He further more closely defines its relations by placing it 

 in the family Euretidae. Certainly the resemblance of the ordinary 

 specimens of Protospongia to my Euhrochus clausus, also a member 

 of the Euretidse, is very great, and at one time, long before the pub- 

 lication of Zittel's monograph, led me to regard them as allied ; 

 fresh facts, however, have since shown me that this view is not 

 correct. 



Caetee considers it probable that both AcantJiospongia of M'^Coy 

 and ProtosjDongia of Salter are the remains of Sarco-hexactinellid 

 sponges. This view, as regards the latter, is entirely confirmed by 

 my own observations. 



Through the kindness of Professor Hughes I have been favoured 

 with an opportunity of fully examining the unique and beautiful 

 specimen of Protospongia fenestrata which has been figured by Dr. 

 Hicks (loc. cit.) and presented by him to the Woodwardian Mu- 

 seum, Cambridge. Dr. Hicks also has himself generously presented 

 me with a number of the ordinary specimens of Protospongia ; and 



