AFFINITIES OF THE GENUS SIPHONIA. 803 



vitreo-hexactinellid sponges, apparently ont of a vague impression 

 that Siplwnia and it are near relations. I merely make mention of 

 the fact here in order to state definitely that Siphonia and Purisi- 

 plionia resemble each other in nothing except their names. 



1872. Pomel, A. ' Paleontologie de la Province d'Oran,' p. 124. 



This author makes a decided advance in regarding the differences 

 in the skeletal tissue of sponges, whether vermiculate or lattice-like, 

 as of fundamental importance ; to the class characterized by the 

 former tissue he refers the Siphonidae ; but he mars the value of 

 this by assigning a calcareous composition to these sponges, a mis- 

 take probably due to his having had before him specimens -which 

 had undergone a mineral replacement. 



Beyond the statement that the Siphonian skeleton is throughout 

 vermiculate, this author, though he writes much, does not appear to 

 add any thing new. 



1872. Nicholson, H. A. ' A Manual of Palaeontology,' p. 70. 

 After a brief description of the genus, Dr. Nicholson gives it as 



his opinion that the Siphonice present a very curious resemblance to 

 the Holtenice (sarco-hexactinellid sponges) of the Atlantic ooze, and 

 were probably, like them, inhabitants of a deep sea. 



"What resemblance there may be lies wholly on the surface and is 

 not very remarkable even there. The ultimate structure of the two 

 genera is as completely different as it can well be ; and the " gise- 

 ment " of most Siphonia* is a greensand deposit, which was laid 

 down, not in the depths of the Cretaceous ocean, but in the shallower 

 waters not far from its shores. " Choanites" however, appears to be 

 the deep-sea form of the genus. 



1873. Thomson, C. WyviUe. « The Depths of the Sea,' p. 486. 



After describing anew species of sponge, Ccelosphcera tubifex*, "an 

 aberrant group of the Esperiadae" (Gray's ?), Prof. SirWyville Thom- 

 son goes on to remark that Choanites may be some relation of this 

 form, on grounds of resemblance which are given in the following para- 

 graph : — " Prom points apparently irregularly placed on the surface 

 of the sponge, tubes about 3 mm. in diameter run out in all directions; 

 the walls of the tubes are thin and delicate, being more so towards 

 the distant ends, where the tubes contract slightly to an open orifice. 

 At the proximal end, at the junction between the tube and the 

 sponge-body, there is also a contraction, and a slight pit-like'involu- 

 tion of the surface of the sponge. There is something very charac- 

 teristic in this peculiar form of junction which it is not easy to 

 define, but which almost forces the conviction that there is the 

 closest relation between these recent forms and tube-bearing fossil 

 sponges such as Choanites" 



The Professor, in his attempts to discover resemblances between 



* Histioderma appendiculaia, Carter, Ami. & Mag. Nat. Hist. ser. 4, vol. xiv. 

 p. 4, pi. 18. 



