156 PEOF. ALLMAN ON NEW HTDEOIDA FROM 



With tlie genus Heteroplon of the ' Challenger ' Expedition 

 it has unmistakable relations in the presence of moveable lateral 

 and fixed mesial nematophores, the mesial nematophores being in 

 both genera separated from the hydrotheca. It differs, however, 

 from IIetero])lon in its dentate hydrotheca- margin in its non- 

 pinnate ramification, and in its pedunculated hydrocladia. 



G-ATTTA HUMILIS, n. sp. (PI. XXIY. figs. 5-7.) 



Tropliosome. — Hydrocladia borne along the length of a creejDing 

 tubular stolon, from which each springs by a cylindrical jointed 

 peduncle, and occasionally sending off a branch which springs in 

 a similar way from the hydrocladium which carries it ; internodes 

 of hydrocladia separated from one another by very distinct 

 joints. Hydrothecse boat-shaped, adnate to the internode by 

 the whole epicauline wall ; aperture with a strong tooth on either 

 side and another in front ; no intrathecal ridge ; mesial nemato- 

 phore short, with a wide cup-shaped termination, separated by a 

 short interval from the hydrotheca ; lateral nematophores trumpet- 

 shaped, supported on short styloid processes which are given off 

 on a level with the hydrotheca-margin. 



Gonosome. — Gonangia pyriform, with broad truncated summit, 

 springing each by a narrow-jointed peduncle from the side of an 

 internode close to the posterior wall of a hydrotheca. 



Locality ? 



Gattya liumilis attains a height of about one fourth of an 

 inch, is the only known representative of its geuus, and pre- 

 sents an assemblage of characters in the highest degree re- 

 markable and distinctive. The peduncles of the hydrocladia are 

 cylindrical, equalling in length a hydrothecal internode, about 

 the thickness of the stolon from which they spring, and com- 

 posed of four or five short annular internodes. Each hydro- 

 cladium is usually quite simple. It occasionally, however, sends 

 off a branch, which then entirely resembles the hydrocladium 

 from which it sj)rings, and to which it is connected by a jointed 

 peduncle quite similar to that by which the primary hydrocladium 

 is connected to the stolon. 



The form of the hydrotheca is very remarkable. It may be' 

 roughly compared to that of a boat, the stern of which is adnate 

 to the supporting internode, while the gunwale carries a pointed 

 process on each side, and the bows are projected into a curved 

 beak. 



