PENNARIA GIBBOSA. 367 



those of the main stem and primary branches, the ultimate ramuli given off 

 at regular intervals from the distal side of the branch, each ramulus increasing in 

 thickness from its base to its summit, and annulated in its entire length ; the 

 hydranths which terminate the main stem and primary branches larger than the 

 others ; body of hydranth bulging obliquely on one side, very tumid at the base, and 

 thence rapidly thinning away towards the mouth in the form of a flask ; filiform 

 tentacles twelve, springing in a verticil from the extreme base of the hydranth ; 

 capitate ; tentacles much shorter than the filiform, about thirty-two in the matm'e 

 hydranlli. 



GONOSOME.- — GoxopiiORES springing just within the verticil of filiform tentacles, 

 each borne on a short peduncle. Medus.e oval oblong, with four globular papillate 

 marginal tentacles. — Ai/assh. 



Habitat. — Growing on submarine objects. 

 BatUymetrkal distriljution. — Lamiiiarian zone ? 

 Locality. — Gulf of Florida, Agassiz. 



I have never seen a specimen of this liydroid, and have compiled my diagnosis from tne 

 description published by Agassiz, who has, moreover, given us a beautiful figure of it, and there 

 can be no doubt that the characters which he assigns to his hydroid must separate it from the 

 European species. It will be seen that while in Gavolini's hydroid the long filiform tentacles 

 spring from a zone, separated by some distance from the summit of the supporting ramulus, they 

 are described as springing from the extreme base of the hydranth in the American species. 

 Agassiz refers to the termination of these tentacles in slightly globular lips, but no indication of 

 this is given in his figure, so that it can scarcely be so well marked as in P. Cavolinii. It will 

 be further noticed that while in P. Cavolinii the ultimate hydranth-bearing ramuli are nearly 

 cylindrical, being but a very little contracted at their origin ; in the American species they rapidly 

 increase in thickness from the base to the summit. 



A remarkable want of symmetry is described by Agassiz as existing in the hydranths of his 

 P. (jihhosa, for he tells us that these " bulge to such an extent on the side facing towards the 

 main stem as to render them strongly gibbous ;" a feature, however, which is scarcely repre- 

 sented in his figure. 



The oldest gonophorcs observed by Agassiz had four marginal, rudimental, knob-like 

 tentacles, but as the generative elements had not made their appearance we have no evidence of 

 the sex of the gonophorcs. On each of the radiating canals, near their distal extremities, Agassiz 

 describes a fusiform swelling, which he regards — though not without some hesitation — as genera- 

 tive sacs like those of the Campanuiarian medusae. There can be no doubt that these bodies are 

 nothincr of the kind ; what they really are, however, it is impossible, with our present knowledge 

 of them, to say. A comparison with the enigmatical swellings already described on the radiating 

 canals of Slabberia, and which have also been erroneously taken for generative sacs, will suggest 

 itself. 



