72 THE PALEONTOLOGY OF MINNESOTA. 



[AnoiualoBpongia . 



plates of the Receptaculitidce than does the knob-like sixth ray sometimes seen in 

 Hyalostelia smithii Young and Young, sp.. and but little better than in the numerous 

 sponges in which the summit ray is wanting entirely. On the whole it compares 

 best with the condition commonly presented by the surface spicules of lithistid 

 sponges. (See fig. \b and c.) 



The next point to be compared is the horizontal rays. A fundamental difference 

 is at once evident in this, that in the Receptoeulitidce there are four of them arranged 

 at right angles so as to form quadrangular interspaces ; while in Anomalospongia 

 there are only three, with the "interspaces triangular. In the Receptaculitidce, too. 

 the horizontal rays overlap not at all or only sparingly, and when they do the over- 

 lapping extremities lie side by side and parallel with each other, and not, as in 

 Anomalospongia, over each other. In the latter the crossing and interweaving of the 

 rays is a marked feature, and not even approximated by the conditions prevailing 

 in the Receptaculitidce. As regards their duplex character in Anomalospongia it suf- 

 fices to say that nothing of the kind is known in any of the Receptaculitidii'. 



The vertical or entering ray of Anomalospongia is on the whole very similar to 

 that ray in Receptaculites, but even more like that in Ischadites, and, if true relation- 

 ship exists between them, it is here that we find it expressed \vith much greater 

 obviousness than in any other feature held in common by them. Still, even here 

 some important differences are apparent. In Ischadites, which as said presents the 

 greatest resemblance to Anomalospongia. and therefore alone need be compared, the 

 vertical rays are entirely separate from each other, and project freely into the 

 central cavity, the continuiby of the wall being formed in part by contact between 

 the horizontal rays, but mainly by the overlapping summit plates. In A. reticulata, 

 on the contrary, each vertical ray is in contact, normally, with six of its neighbors, 

 so that the task of maintaining the shape of the sponge, was performed chiefly by 

 this part of the spicules. 



Other points of difference are noticed in the uniform size and in the arrangement 

 of the spicular elements of Anomalospongia when compared with the true Receptacu- 

 litidft'.* In the latter they are small at the nucleus and increase gradually in size to 

 the periphery ; with the arrangement in regular curved intersecting lines closely simu- 

 lating a common style of engraving on watch cases. In Anomalospongia, however, 

 the pieces are of nearly the same size on all parts, and the arrangement that merely 

 which would result from placing equal hexagonal pieces in contact with each other 

 on all sides. 



A feature in which Anomalospongia agrees with Receptaculites, but not more so 

 than with other very different sponges (Geodia clavata Hinde), is the peculiar neck-like 



*Not applicable t.. X/r/vwponfffn, Pengelly. wHIrh it seems to me lias lltlli' I'laim to association in the same family with 

 ReceptamMcH. 



