FROM THE INFERIOR OOLITE. 547 



LITHISTID^E. 

 RHIZOMORINA. 



Platvchoxia elegaxs. sp. nov. (Plate XXI. figs. 22-25.) 



Sponge a thin, irregularly undulating plate, with an irregularly 

 curved margin, growing out into lobes which sometimes overlap. 

 Upper surface irregularly ridged and dimpled, ridges occasionally 

 growing up into angular lobes, smooth ; lower surface rough, but 

 less dimpled. Thickness of plate -J inch, becoming less towards 

 the rounded margin ; in the specimen from which the description is 

 taken the length and breadth of the plate are 5 inches and 4 inches 

 respectively. Canal -system absent. Skeleton apparently consist- 

 ing chiefly of Rhizomorine elements, often arranged in groups form- 

 ing fibres ; but Tetracladine forms are frequently present. 



Log. Burton Bradstock. 



Hot. Upper part of the A. ParJcinsoni-zone. 



Obs. The skeletal elements are not very well preserved, so that 

 they do not as a rule appear sharply defined from the surrounding 

 matrix, and thus their tubercular and Pkizomorine character may be 

 more apparent than real, the result merely of subsequent changes. 

 Where they occur exceptionally well defined, they almost always 

 present a quadriradiate outline (triradiate in section), with smooth, 

 almost cylindrical rays, terminating, either immediately or after 

 once bifurcating, in an irregular mass of calcite, which represents 

 the interlocked ends of a number of conjoined elements. From 

 this one is tempted to infer that the sponge rightly belongs to the 

 Tetracladina ; but since the distinction between this family and 

 the Rhizomorina rests rather on the presence of Phizoniorine than 

 the absence of Tetracladine elements, I have, though w r ith some 

 doubt, referred it to the latter ; and I have been the more readily 

 led to this assignment because Prof. Zittel has similarly referred to 

 the Phizomorina sponges so precisely similar in all their characters 

 to that under consideration, that, without quite positive evidence to 

 the contrary, I would not venture on a different determination, 

 which would, moreover, involve the institution of a new genus. 



INCERTJS SEDIS. 



The following sponges belong to Zittel's Pharetrones. Their 

 fibres, so far as they exhibit structure, all present us with tri- and 

 quadriradiate spicules, many of large size, their rays being 0*01 inch 

 long and 0*001 in diameter ; besides these, smaller spicules of unde- 

 termined character are present, I have devoted much time and 

 attention to the study of these sponges without arriving at anj- 

 positive conclusion regarding their true affinities. They may be 

 allies of Tricentrium, or Tetractinellidas, forming a passage between 

 the Choristidae and Lithistidse; or, on the other hand, they mav 

 very possibly be, as Prof. Zittel maintains, genuine Calcispongiffi. 

 Further research alone can decide. No further light is thrown on 

 the matter bv their mineral state : like the undoubted Lithistid and 



