[MATiHEw] STUDIES ON CAMBRIAN FAUNAS 107 



HELENIA, Walcott. 



Mr. Walcott discovered a curious flattened tube in the conglomerate 

 limestone at Manuel's Brook. From the fact that it was open at both 

 ends he referred these tubes to Dentaliidse. Though I have not seen 

 the species described by that author I have met with a fossil which 

 seems related to it. The flattened elliptical form of the tube makes one 

 suspect a relation to Torellolla, but we find no evidence that the shell was 

 phosphatic ; it is very thin, and appears to be of a calcareous composi- 

 tion, we have therefore used Walcott's generic name, but would not refer 

 the Etcheminian form to the Dentalidte, but rather would suppose it 

 related to the tube worms. Some of the sea worms have quite flat bodies 

 (especially some parasitic forms). 



HeLENIA GRANUIiATA (PI. VI,, figs. la to e). 

 Helenia granulata, Nat. Hist. Soc, Bull. No. xviii., p. 192, pi. il., figs, la to e. 



Small, much flattened, curved tubes ; the curve not in one plane, 

 but the tube somewhat twisted. The tubes enlarge toward the orifice so 

 that in a distance of 10 mm. in the smaller pai't of the tube the long 

 diameter is doubled. 



Sculpture. — The surface is minutely granulated. 



Size. — Only fragments of 10 mm. and less are known. The widest 

 section is "A^ mm., diminishing to \ mm. This is the longer diameter ; 

 the shorter is a fifth to a seventh of this, the tube becoming more flattened 

 toward the aperture. 



The peculiar curve of this shell, which is mostly parallel to the flat- 

 tening of the shell, not at right angles to it, as in Hyolithes, distinguishes 

 it from all its associates. In this it resembles the pleural or genal spines 

 of trilobites, but we have not found in association any other parts 

 of trilobites. 



HYOLITHELLUS, Billings. 



The history of this name is a singular one, and to me the actual 

 genetic relation of the objects included under it is obscure. 



In 1872, Mr. Billings found a slender cylindrical object in the con- 

 glomerate limestone of Troy, N.Y., under this name separating it from 

 Hyolithes on account of its long slender form and peculiar (supposed) 

 operculum.' 



In the following year appeared Prof. James Hall's description of 

 the genus Discinella, which was based on the object which Billings had 

 described as the operculum of Hyolithellus.^ 



1 Can. Naturalist, New. Ser., vol. vi., p. 240. 



2 23rcl Rep. New York State Museum of Nat. Hist., p. 246. 



