M. K. A. Zittel on Fossil LitMstidce. All 



SiPHONiA, Park., 1822 *. 



Cancoides, Guett. 

 Siphonia p. p., Park, et auct. 

 Clioanites p. p., Mant. 

 Hallirhoa, Lamx. 



Siphoneudca and Polysiphoneudea, From. 



Siphonia, Hcdlirhoa, Angidia p. p., Plethosijjhom'a, Polysiphonia, Ptero- 

 calpia, ?Physoc(dpia, Pomel. 



Sponge ficoid, pyriform or pomiform, sometimes rendered 

 lobular by constrictions, generally simple, with short or long 

 stalk, rarely stalkless. Vertex with a deep central cavity, on 

 the wall of which ai-e the round ostia of efferent canals, usually 

 arranged in longitudinal and transverse rows. These rather 

 wide canals are curved parallel to the outer contour of the 

 sponge, but become more and more upright towards the mid- 

 dle, and finally vertical, being continued into the stalk and 

 root as bundles of tubes. The curved canals decrease in size 

 outwards, and commence at the surface in several fine tuber- 

 cles, which unite and then run to the cloaca. Numerous 

 smaller afferent canals run obliquely from within outwards, 

 cross the curved canals, and commence at the surface in 

 depressed round ostia. 



Skeleton formed of large, distinctly quadriradiate corpus- 

 cles. The arms are smooth or slightly tubercular; their ends 

 divide into two, three, or more branches with root-like pro- 

 cesses. The corpuscles are usually arranged serially along 

 the course of the canals ; and their thickened and interlocked 

 ends form regular radial bands f. Large bacillar spicules 

 occur at the surface, in the canals, and in the skeleton ; 

 anchors with forked prongs are rare. 



Many species of this genus change their form as they 

 increase in size. Young specimens are generally cylindrical 

 and traversed by nearly vertical tubes. The changes are 

 figured by Sowerby (Geol. Trans, ser. 2, vol. v. pi. xv.) in 

 Siphonia tulipa. 



Externally SipJionia very closely resembles Jerea. The 



* Mr. Sollas lias puMislied a paper in the Quart. Journ. Geol. Soc. 

 vol. xxxiii. p. 790, in which he treats of the structure and affinities of the 

 genus Siphonia. The author remarks that he agrees with INIr. Sollas in 

 all essentials, and that the latter has given fuller particulars ou some 

 points than will be foimd in the fir.st section of the present memoir. 

 The author separates Jerea from Siphonia, which jNIr. Sollas has not 

 done. 



t The microstructure nf the root agrees generally with that of the rest 

 of the skeleton, exc-pt in the species with long stalks, in which the arms 

 of the corpuscles, or one nf them, are much elongated. See also Sollas, 

 Joe, dt. 



