M. K. A. Zittel on Fossil Lithistidce. 115 



of German naturalists at Munich in September 1877*, made 

 communications upon the organization, microstructure, and 

 geological distribution of the fossil Hexactinellidse and Lithis- 

 tidse, and illustrated them by the exhibition of microscopic 

 preparations and numerous drawings. 



This, so far as I know, is all that has hitherto been published 

 about the occurrence of fossil Lithistidge. The literature of 

 the living representatives of this group is also of but small 

 compass. The first forms belonging to it were described 

 bj Johnson f. Gray J, Bowerbank §, and Bocage ||, but, not- 

 withstanding the peculiarity of their structural characters, 

 were not separated from the other marine sponges with a 

 vitreous (siliceo-fibrous) skeleton. It was only in the year 

 1870 that the examination of several species, newly discovered 

 in the Atlantic Ocean, led Oscar Schmidt^ to establish a 

 distinct order of Lithistidce. Oscar Sclimidt characterizes as 

 Lithistidas (Z. c. p. 21) "the sponges Avith coherent siliceous 

 tissue, the spicules of which do not grow in accordance with 

 the triaxial type, but form an apparently quite irregular com- 

 plication. In this, generally, a centrifugal and a concentric 

 primary direction is recognizable, which, however, does not 

 express the influence of a dominant spicular type, but adapta- 

 tion to the general conditions of currents. Although their 

 sarcode possesses properties which approximate them, to some 

 extent, to the Hexactinellidse, and, with these, probably to the 

 fossil sponges, they approach very closely to the (other) 

 living sponges in the canal-system, which is very indistinct 

 in the former group. In external form there is no agreement 

 within the family ; but cup- and bowl-shaped species abound." 



What this character wants in sharpness and definiteness is 

 supplied by the careful descriptions and figures of eight 

 species, which 0. Schmidt distributes between the three 

 genera Leiodermatium, Coralh'stes, and Lyidium. 



H. J. Carter has published a complete summary and critical 

 discussion of all the Lithistidse known up to the year 1873 **. 

 In this admirable memoir the characters of the Lithistidse are 

 established more clearly than by O. Schmidt, and the whole 

 group is characterized as follows : — " Spicules developed upon 



* Amtl. Ber. iiber d. 50. Versamml. deutsch. Naturf. und Aerzte iu 

 Munclien, 1877, p. 161. 



t Proc. Zool. Soc. Lond. 1863, p. 257. 



X Ibid. 1859, p. 437, pis. xv., xvi. ; 1867, p. 507 ; 1868, p. 5C5. 



§ Ibid. 1869, pp. 66-100, pis. 3-6, and p. 323. 



II Journ. Sci. Math. Phys. et Nat. Lisb. 1869, uo. iv. 



^ Grundz. Spong. atlant. Geb. 1870, p. 21. 



•• Ann. & Mag. Nat. Hist. ser. 4, vol. xii. (1873) pp. 349-373, 

 437-472. 



8* 



