SPONGES, GRAPTOLITES, CORALS. 



A iiomalospongia.] 



a glass of low power, especially in a side light, the surface of such specimens appears 

 to be striated longitudinally. But when the surface is perfectly clean the oblique 

 rays are to be seen dipping under the longitudinal rays. 



We now come to the consideration of one of the most peculiar features of 

 Anomalospongia, namely, the duplex character of the horizontal rays. Each is in 

 fact divided into two subcylindrical equal parts by a sharply impressed central 

 groove, extending from the central node to their distal extremities. It is not pos- 

 sible that these grooves (theie is one on both the upper and lower sides of the rays) 

 can have resulted from pressure, because the condition is too uniform. And I have 

 detected no sign whatever of fractures that would necessarily have resulted from pres- 

 sure. Nor can I see how a cylindrical ray with a large axial canal, such as we would 

 be obliged to assume in that case, could be compressed so as to become equally 

 grooved on both the upper and lower sides. No, after viewing the matter from 

 all sides, I see no other way than to accept the evidence as presented by the speci- 

 mens. After that I believe we are warranted in assuming (1) that the duplex char- 

 acter is a peculiar form of bifurcation, (2) that the axial canal is small and (3) 

 dividing at the node, ran independently up each half of the ray. A diagrammatic 

 representation of the parts is given in the accompanying cut (fig. 1). 



Fig. 1, a, diagrammatic representation of the inner part of the horizontal rays of a spicule of Ano- 

 malospongia rcticulata, showing the supposed bifurcation of the rays and axial canals. 6 and c, 

 highly magnified top and side views of a surface spicule of a recent lithistid sponge. (Corallistes 

 microtuberculatus Schmidt .) 



The sponge was probably originally siliceous, but the specimens as now pre- 

 served are crystalline calcite. 



As regards the systematic position of Anomalospongia the Receptaculitidce are 

 deserving of first consideration ; not so much because of a closeness of relationship 

 as that "Anomaloides" has been referred to that family, indeed, a certain author has 

 been indiscreet enough to place that name among the synonyms of ReceptacuUtes! 



The first essential of the Receptnculitidtt' are the rhomboidal or hexagonal summit 

 plates, which have been regarded by Hinde (see q notation ante p. 55) perhaps cor- 

 rectly, as modified spicule rays. 



In Anomalospongia the abortive fifth ray is reduced precisely as in some hexac- 

 tinellid sponges, to a mere knob, and therefore compares no nearer with the summit 



