RELATIONS OF SAGITTA 13IPUNCTATA. 25 



of the lateral fins will afford most useful diagnostic characters, 

 describes the following; species: — 



1. S. multidentata (Wieg. Arch. 1853, p. 271, Plate 12, fig. 

 2). — Which in habit closely approaches the S. setosa of Wilms 

 (our S. hipunctata). The posterior fins are longer and wider 

 than the anterior, which extend in front to about the anterior 

 third of the body. The number of hooks is from 9 to 11. That 

 of the denticles in front of the mouth (fig 3, «), is in the ante- 

 rior row from 5 to 8, and in the posterior from 12 to 13. 



He notices another form closely resembling the above, 

 but characterized by the existence of a horny, toothed ring 

 around the orifice of the ejaculatory sacs. 



2. S. serrato-dentata (1. c. figs. 3 and 4). — Which appears to 

 resemble the foregoing in nearly all respects, except in the 

 conformation of the hooks, which are described as serrated on 

 the inner edge for about half their length. The number of 

 hooks is from 6 to 8 on either side. The denticles in the an- 

 terior row are never more than eight in number on each side, 

 whilst in the posterior there are as many as 18 The bundles 

 of rigid setce are disposed symmetrically in eight lateral rows, 

 four dorsal and four on the ventral aspect. It is a very small 

 species, not exceeding 4^ m. in length. 



3. S. hjra (1. c., fig. 5). — The caudal portion of the body 

 very short and separated by a groove from the elongated 

 trunk. The two pairs of lateral fins are apparently continuous 

 with each other, and the anterior are much longer than the 

 posterior, and extend far anteriorly. The number of hooks 

 is 6 to 8 on either side ; of the denticles, 7 in the anterior 

 and 11 in the posterior series. The bundles of setce are irre- 

 gularly distributed over the surface of the body. It is a large 

 species, attaining the considerable length of from 3 to 3^ 

 centim. 



4. S. draco (1. c, fig. 6). — The body of this rare form is 

 short and thick, and invested for the anterior three-fourths of 

 its length, by a very considerable layer of large, thick-walled 

 cells. The caudal portion is very long, the trunk short, and 

 the caudal fin of large size. The anterior pair of lateral fins 

 is wholly wanting, and the pair corresponding to the pos- 

 terior fins of other species do not extend beyond the caudal 

 portion of the body. The species is remarkable also for the 

 existence of two lateral and opposite bundles of numerous, 

 very long, freely-floating filaments, seated upon special emi- 

 nences, which again are placed upon the cellular layer sur- 

 rounding the anterior part of the body. The filaments are of 

 soft consistence, ligulate, and constituted of parallel longitu- 

 dinal fibrillae. There are ten hooks on either side ; eijjht 



