DOUBTFUL SPECIES. 329 



Hydraxths slender, retractile, witli eight long muricated tentacles, held alternately, 

 elevated and depressed. 



GONOSOME. — GoNOPnORES pear-shaped, or sub-globular, borne by the liydro- 

 caulus in groups of two or three together; medusa "globose, slightly truncated below, 

 with a contracted aperture ; four moderately sized sub-clavate tentacles arising from 

 four semicircular yellowish lobes at the margin of the umbrella ; sub-umbrella small, 

 with four radiating canals, the centre occupied by a mass of yellowish or orange 

 granules, apparently ova; ])eduncle (manubrium) inconspicuous, branched at the 

 base." — Alder. 



Ilahitnl. — On TvrriteUa communis and other shells. 

 Bal/ij/metrical disirihufio/i. — Deep-water zone. 

 Loccdiiy. — Coast of Northumberland, Mr. Alder. 



It is with great hesitation that I refer tins species to the genus Pcriyonhnus. I have never 

 seen it, and the characters given above are those assigned to it by Mr. Alder. So far as the 

 trophosomc is concerned, there is nothing to exclude it from Perifjonimus, but if the medusa bo 

 correctly described, there is some reason for regarding it as belonging to a distinct generic 

 group. 



The characters of the medusa, howevei', are not given with sufficient detail and precision to 

 afford material for the definition of a new genus. Indeed, it seems pretty evident that the 

 medusae of the specimen which furnished the subject of Mr. Alder's description and drawing were 

 not in a perfect state, that they had undergone more or less change from exposure to unfavorable 

 conditions, and that their essential characters had been thereby obscured. We must wait, 

 therefore, until further observations shall have made us better acquainted with its gonosome, 

 before we can venture upon a precise characterization of this curious little hydroid. Until then 

 we may retain it in the genus Periyonimus, to which it appears to come nearer than to any other 

 genus hitherto defined. 



DOUBTFUL SPECIES. 



The " Atr.\ctylis bitentaoulata" of Wright (' Proc. Roy. Phys. See./ Edin. for Feb., 1S63, 

 p. 43, pi. i, fig. 5), and the " Atractylis quadritentaculata" of Wright [id. fig. C) are probably 

 immature forms of some species of Perigonimus. In the absence, however, of all knowledge of 

 the gonosomes it is impossible to assign them with certainty to any established genus. 



They are very small forms. The " AtradijUs bitentaculatd' is described as consisting of 

 minute, nearly sessile hydranths, springing from a retiform hydrorhiza, and furnished each with 

 two erect tentacles. The hydrantlis " have a habit somewhat like that of Lar, of quickly 



