516 M. K. A. Zittel on Fossil HexactinelUda. 



1877, in the Matliem.-PIiysical Class, and immediately after 

 sent to press. In the beginning of February, the January 

 number of the ' Annals and Magazine of Natural History ' for 

 1877 reached me, which contains a memoir by W. J. Sollas 

 "On Stauroyiema^ a new Genus of Hexactinellid Sponges, with 

 a Description of its two Species, St. Carteri and St. lobata.^'' 



Mr. Sollas describes very fully the external form, the con- 

 struction, and the microstructure of the lamelliform sponge- 

 body, the lateral margins of which are somewhat bent round, 

 and in conclusion devotes much attention to the state of pre- 

 servation and the peculiar phenomena of fossilization occurring 

 in these petrifactions. I cannot refrain from referring to this 

 work of Mr. Sollas with particular satisfaction. He is the 

 only palseontologist whose mode of investigation agrees in 

 general with that adopted in the preceding memoir, as also 

 in my monograph of CoelojitycMum ; and it is certainly in 

 favour of its admissibility that two observers, writing quite 

 independently, arrive at the same result in all essential points. 



In August 1876, at the general meeting of the German 

 Geological Society at Jena, in a lecture on the organization 

 and classification of fossil sponges*, I indicated, with the aid 

 of numerous drawings made from microscopic preparations, 

 the close agreement of certain living and fossil Hexactinellida, 

 and at the same time discussed the conversion of the originally 

 siliceous skeleton into calcsparf, which is so frequently ob- 

 served in fossil Hexactinellida and Lithistida. In conversa- 

 tion, many objections to this chemical substitution were 

 expressed to me. It appears to me therefore worthy of 

 notice, that on this question Mr. Sollas expresses precisely the 

 same opinion ; his observations with respect to the optical 

 behaviour of the fossil skeletons of Hexactinellida also per- 

 fectly agree with mine \. 



As regards the genus Stauronema^ which is at present known 

 only from the Gault of Folkestone and the Upper Greensand 

 of the Isle of Wight, it is most nearly allied to Aphrocallistes. 

 From Mr. Sollas's detailed description and figures I have been 

 able to draw up the diagnosis of the genus (seep. 506). 



In conclusion, I may remark further that Mr. Sollas regards 

 the Stromatoporce § as Hexactinellida, an opinion which I can- 

 not share. The zoological position of Stromatopora and 

 Parkeria appears to me to be scarcely doubtful after the acute 

 investigations of Carter ||. According to these the above-men- 



* Zeitschr. d. deutsch. geol. Gesellsch. xxviii. p. 631. 

 t See this Memoir, pp. :364-6, 



X Sollas, /. c. p. 21. § Loc. cit. p. 2. 



I! Ann. & Mag. Nat. Hist. 1877, vol. xix. p. 44. 



