^70 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



Occurrence. — Camden chert, Camden, Tennessee. 

 Cat. No. 35,089, U. S. N. M. 



RHOPALONARIA TENUIS new species 

 (Plate LXVI, 7, 8, 9) 



Fusiform cells attenuate, averaging about 3 in 2.0 mm., occasionally 

 only 4 in 3.0 mm. ; greatest diameter of same about 0.5 mm. On the 

 best specimen many of the cells preserve remains of the pores. Of 

 these there is usually only one situated near the center of the cell, but 

 in others there appear to be two pores. The connecting stolons 

 rarely equal the fusiform swellings in length, the average, however, 

 is considerably less. 



The general aspect of the colony is greatly like that of R. vcnosa, 

 but when critically compared the fusiform cells of the Devonian 

 species prove to be both narrower and longer, and the connecting 

 stolons generally shorter than the Ordovician type of the genus. In 

 the Silurian species, R. attenuata, the fusiform swellings, though 

 about equally narrow, are considerably shorter and enlarge more 

 abruptly, while the connecting stolons are much longer. 



The original of figure 9, plate lxvi, is doubtfully referred to 

 this species. It consists of the excavations only, but these are so 

 closely arranged that it is difficult to make out the series. Evidently 

 several branches cross each other. 



Occurrence. — The figured type is from the lower shales of the 

 Hamilton formation at Thedford, Ontario. The species also occurs 

 in the same formation at Alpena, Michigan, and Eighteen-]\Iile creek, 

 New York. 



Cat. Nos. 43.118, 43,119, and 43,121, U. S. N. M. 



RHOPALONARIA MEDIALIS new species 



(Plate LXVI, 10) 



Compared with other species the colonies of this form appear less 

 compact and the arrangement of the cells more straggling. In the 

 matter of size, the fusiform cells are more robust than in any of the 

 other forms except R. rohusta, the position of the species in this 

 respect being almost exactly intermediate between R. rohusta and 

 R. venosa. About 4 of the cells in the middle series occur in 3.5 mm., 

 while of those in the lateral branches the average number in an equal 

 space is about 5. The connecting stolons are rather short, the aver- 

 age length not exceeding two-thirds that of the fusiform swellings. 



Compared more particularly with the associated R. tenuis, it is 

 distinguished at once by its more robust aspect and looser habit of 

 growth. 



