AFFINITIES OF THE GENTJS SIPRONIA. 823 



The distribution of the Lithistid sponges is of interest as resem- 

 bling and throwing light on that of the SipJionice : bathymetrically 

 they range from 75 to 374 fathoms (Carter), or 152 to 270 (Schmidt); 

 geographically they are found in the Atlantic, about the West Indies, 

 Madeira, the Azores, and the coast of Portugal. The Siphonim simi- 

 larly occur most abundantly in Greensand-beds, which were laid 

 down not very far from the shore-line of the Cretaceous sea, and at 

 not excessive depths from its surface. Here then is another link 

 between the modern and the Cretaceous Atlantic. The specimen of 

 S. piriformis described by Goldfuss, from the Jurassic, I must leave 

 to Sir Wyville Thomson and his supporters. 



Class SPOXGIDA. 



Order HOLORHAPHIDOTA. 



Family PACHASTRELLID^E. 



Group LlTHISTINA. 



Genus Siphonia. 



Synonyms : Carico'ides, Guettard ; Hallirhoa et in parte Jerea, 

 Lamx. ; Polypothecia, pars, Benett ; Choanites, Mantell. 



Sponge. Consists of a head or body of variable shape supported on 

 a longer or shorter stem, by which it is attached to some foreign 

 body, or without a stem and anchored by a number of diverging 

 rooting fibres which penetrate the silt in which it is imbedded. 



Canals of two kinds, excurrent and incurrent, the former longi- 

 tudinal, opening distallyin oscules situated on the walls of a central 

 cloaca, or upon a plane surface at the summit ; the latter radiating, 

 opening externally in pore-areas, and internally into the excurrent 

 canals. 



Skeleton siliceous; sjncides (1) staple, quadriradiate with four 

 diverging arms, all of which are smooth and round, bifurcating near 

 their extremities, and terminating in a number of rounded apophyses 

 with intervening Concavities. Combined into a rigid network by the 

 interlocking of their apophysial endings, and arranged in bands 

 parallel to and chiefly about the radiating canals, the smooth arms 

 lying concentrically, and their terminations forming a series of 

 radiating bands of filigree. (2) Smooth acerate spicules, lying 

 parallel with the series of staple spicules. (3) Flesh-spicules (?), 

 (4) Dermal spicules (?), not found attached to the sponge, but 

 occur in association in the Haldon Greensand. 



Formation. Cretaceous and Jurassic. 



Locality/. England — Haldon, Blackdown, Wilts, Isle of Wight, 

 Sussex, Yorkshire (?) ; Germany — Coesfeld, Quedlinburg, Borzen, 

 Kutschlin ; France — Cognac, Tours, Honfleur, Rouen, Havre, St. 

 Aignan, Saumur; Russia — Bouchevoe (near Moscow). 



Species. S. pi/riformis, costata, Webtsteri, Konigii, and arbtiscula. 



3h2 



