40 BULLETIN 16 4, UNITED STATES NATIONAL MUSEUM 



CAMAROCLADIA PLANA, new species 



Plate 11, Figuees 7, 8 



Description. — Sponge flat and rather broad, branching dichoto- 

 mously, the diameter of the stems varying from 2 to 6 mm. The 

 surface of the stems is fairly smooth and is covered irregularly 

 by countless microscopic pores with a few rather large ones. The 

 general features of the section are identical with those in C. fucoides. 

 Ulrich and Everett originally defined G ainarocladia as " sponges 

 consisting of small subcylindrical branching stems. * * * s This 

 flattened specimen might, therefore, belong to another genus, but 

 since both external and internal features, except only the flatness 

 of the stems, practically coincide with like characters in the geno- 

 type, G. dichotoma., I have placed it in C amarocladia. 



Formation and locality. — Same as preceding. 



Holotij'pe—\}.^:^M.. No. 83624. 



Genus STROMATOCERIUM Hall, 1847 



STROMATOCERIUM REGULATUM. new species 



Plate 11, Figuees 1-3 



Description. — The specimens referred to this species form large 

 hemispherical or subglobular masses, frequently 25 cm or more in 

 diameter with a comparatively smooth surface on which the mamil- 

 lary elevations are not so well marked. Under an ordinary magni- 

 fier the structure in vertical section is seen to consist of a succession 

 of thin concentric layers resting on varying thicknesses of interme- 

 diate vesiculose tissue, and both structures are penetrated by vertical 

 pillars. The pillars appear as rather short and narrow lines and 

 are not continuous throughout the entire height of the coralline 

 growth, but appear and disappear at irregular intervals. The pil- 

 lars grow in fascicles, those of the same fascicle spreading upward 

 and outward from the center of the fascicle toward the surface of 

 the specimen. The tangential section exhibits rather irregularly 

 arranged pores and shallow stellate furrows (astrorhizae), which 

 radiate outward from several centers. 



Gomparlsons. — In general, this species appears very much like S. 

 rugosuvi Hall from the Black River formation of North America, 

 but the comparatively more regular concentric layers, the rather 

 more closely spaced intermediate vesiculose tissue, and the more pro- 

 nounced i^illars serve to distinguish it. On the other hand, this 



• Ulrich and Everett, Geological survey of Illinois, vol. 8, p. 20, 1800. 



