282 Systematic Paleontology 



Occurrence. — Helderbeeg Formation, Xew Scotlaxd Member. 

 Devil's Backbone, Corriganville. 



Collections. — Maryland Geological Survey, U. S. Xational Museum. 



Fenestella (Cycloporina) altidorsata n. sp. 



Plate XLV, Fig. 15 ; Plate XLIX, Figs. 1-3 



Description. — Zoarium apparently not infundibuliform, but growing 

 from small attachments into large flabellate expansions, 2 inches or more 

 in diameter. Judging from material in hand these expansions on con- 

 tinued growth become irregular in outline and perhaps folded so that the 

 fossilized network, which sometimes covers the space of a man's hand, was 

 matted together with the branches of overlying parts oriented in varying 

 directions. Aside from this largely fortuitous irregularity, the branches 

 impress one as fairly rigid. Their number in a given space varies from 

 the fact that twu or more adjacent branches will bifurcate almost simul- 

 taneously. One of the fragments on the slab shown in fig. 2 of pi. xlix 

 shows five branches thus simultaneously divided, anotlier three. How- 

 ever, a fair average would be 13 or l-t in 10 mm., with extremes ranging 

 from 12 to 16. The fenestrules vary in width for the same reason, but 

 measured longitudinally their number in 10 mm. is constantly 6 or 7. 

 Of zooecial apertures 22 or 23 are counted on each side of a branch in 5.0 

 mm. Not only the branches, but the dissepiments also are carinated. 

 The branches and carinas grow stronger with age, the latter being veiy 

 prominent on the older portions of the colonies. A striking feature of 

 the species is that the carinas are developed on both the obverse and the 

 reverse sides, though usually not so sharp on the back as on the front of 

 the branches and dissepiments. The development of carina on both 

 sides of the zoarium, coupled with the fact that the branches appear 

 nearly as rigid on the reverse as on the obverse side, is likely to cause 

 some difficulty in distinguishing tlie two sides, especially when the 

 specimen is sufficiently imbedded in the nuitrix to obscure the zooecial 

 apertures. An occasional feature, retained, however, only bv the most 

 perfect examples, is the presence of relatively large semicircular caps 



