56 THE VOYAGE OF H.M.S. CHALLENGER. 



Calyptrophora josephinse, Lindstrom,' with the polyps beut downwards. It is also 

 possible that Primnoa regularis, Duchassaing and Michelotti," not only belongs to this 

 genus, but an inspection of the remains of the original specimen in the Turin Museum 

 makes it just possible that Stachyodes regularis equals Primnoa regularis. For this 

 species Dr. Gray has made the genus Narella,^ and places it between Stenella and Prim- 

 noella. The definition is, however, unintelligible, and is certainly not diagnostic of the 

 species from Guadeloupe. Dr. Studer emended the diagnosis of Dr. Gray's genus, and 

 included in it two new species,* which would not be included in Stachyodes. Dr. Kolliker 

 includes Primnoa regidaris, D. and M., among the species of Primnoa as diagnosed by 

 him,' and, from the measurement of the spicules of the polyp given by him, these would 

 in the form from the Atlantic indicate a smaller species than the one now described 

 from the Pacific Ocean. 



Genus 3. Stenella, Gray {emend.). 

 Stenella, Gray, Cat. Lithophytes Brit. JIiis., p. 48, 1870. 



This genus was established by Dr. Gray for Primnoa imhricata, Yate Johnson. A 

 comparison of the type species shows that it has very close affinities to Thouarella, which 

 was established by the same author for Primnoa antarctica, Val., and it is possible that 

 a more extended knowledge of the species will result in the two genera being merged 

 into one. For the present the arrangement of the polyps on the branches will serve as 

 a convenient distinction. In Stenella they are opposite and in whorls, in Thouarella 

 they are alternate and arranged in spirals. The axis is hard, in a young stage horny, 

 fibrous, but soon becomes dense with calcareous material; under the coenenchyma it is often 

 highly iridescent. The base, so far as known, is attached by a calcareous disc to Corals 

 or stones. The axis is feebly or much and irregularly branched. The coenenchyma is 

 thin, with large disc-like spicules, often deejjly concave with turned up edges, and attached 

 to the coenenchyma by the central concave portion. In an attached specimen a thin 

 ]ayer of coenenchyma with spicules spreads over the Coral to which the Stenella axis 

 adheres. The polyps are large, prominent, in whorls of two or four. The bodies of the 

 polyps are enclosed in several rows of large, imbricating scale-like spicules, of which the 

 row (preopercular) just below the opercular scales, foi'ms a more or less complete in- 

 vesting calyx. The opercular scales are eight in number, symmetrical, and fold com- 

 pletely over the retracted tentacles. Sometimes they form a conical and projecting, at 

 other times a more or less flattened operculum. 



■ K. Svensk. Vetenslc. Akad. Handl, Bd. xiv. No. 6, p. 6, 1877. 



2 Duchassaing et Michelotti, Mem. sur les CoraUiaires Jes Antilles, p. 17, pi. i. figs. 12, 13. 



' Cat. Lithophytes Brit. Mus., p. 49. 



■• Monatsher. d. k. preuss. Alcad. d. fViss. Berlin, 1878, p. 643. 



^ Icones Histiologies, p. 135, 1865. 



