384 



Report of the State Geologist. 



(loc. fit. fig. 1). The separation is of such a nature that only the cylindrical 

 rods adhere to the gastral cast while the anchorate spicules and denies 

 are beautifully displayed in their original position upon the enveloping 



matrix. The secondary vertical lateralia 

 and the horizontal reticulating bands are 

 composed of comparatively few cylindrical 

 spicules, some of which attain a greater 

 size than any observed in the principal 

 lateralia, but neither of these series has 

 shown any trace either of the anchorate or 

 of the clemate spicules. 



Mention has been made of the radiate 

 tufts produced by the extension of the 

 horizontal spicular rods at their intersec- 

 tion with the vertical lateralia of both 

 series. The spicules of the horizontal 

 lateralia appear to lie nearer the gastral 

 surface than do the principal and secondary vertical bundles. At the intersec- 

 tion of the horizontal and vertical bundles are occasionally seen large pentacts, 

 sending a ray along each bundle departing from that point, the fifth ray 

 passing inward. These pentacts are the heaviest parts of the skeleton, and 



as they lie above or outside of 

 the lateralia they probably belong 

 to the dermal surface. 



The dermal surface of the 

 quadrules formed by the intersec- 

 tion of the lateralia is regularly and 

 very finely reticulated by smooth- 

 rayed pentacts lying in apposi- 

 tion. These vary in size but are 



Figure 42. Physospongia Dawsoni. A somewhat diagrammatic flg- ,1 -i -i 



ure of one of the. sp icuiar tufts, no. <j. m. c.) never more than one-tenth as large 



as the smooth pentacts at the intersection of the lateralia. Among the spicules 

 which evidently belong to the parenchyma of the sponge are numerous frag- 

 ments of echinate branches, some of which undoubtedly are parts of echinate 

 hexacts, as that represented in figure 41. The same figure shows a fragment 

 of a large spicule in which the surface spinules are more produced than in any 

 of the echinate spicules of other species. This form of spicule seems to be of 

 rare occurrence in the species, and from analogy with P. Colletti, GlebcUctya 



Figure 41. Spicules of Physospongia Dawsoni, X400. 

 Fragments of echinate hexacts, a smooth-rayed pentact, 

 a diact and part of a cleme. (J. M. C.) 



