58 DE. G. H. FOWLER — BISCATAN PLANKTON : 



himself on safe ground. As a secondary character, I find the form of the vestibular 

 ridge, which lies just in front of the jiosterior teeth, to be of assistance. In many 

 cases below, the anterior and posterior teeth have been figured, but I doubt whether 

 such draAvings have much value ; the teeth look so different when viewed at different 

 angles. 



Examination of the ' Research ' Specimens. 



Tlie first hauls examined were dealt with very carefully ; the dimensions of every 

 specimen taken, and the jaws and teeth counted, until every common species had the 

 look of a familiar friend. After that, the epiplankton hauls were sorted, chiefly by a 

 dissection-lens, measurement and counting being done only in cases of doubt, or as an 

 occasional check on sorting by eye. Of the mesoplankton hauls, on the other hand, 

 every specimen (except a few young zetesios) was measured and counted and identified 

 with care. When the whole collection had been thus sorted into species, every specimen 

 was re-examined; and as there were over 2100 specimens, the task has not been 

 light. 



It is therefore possible, though not likely, that a few " hexaptem ? " have been mistakenly 

 assigned to furcata. Mistakes are esj^ecially likely to occur with very young specimens 

 (one species excepted), and they have therefore not been recorded when in the least 

 doubtful : small specimens are often impossible of determination in the jn-esent state of 

 our knowledge, because the numbers of jaws and teeth are then small, and the 

 proportion of tail to trunk is generally higher than in older specimens ; even the 

 character of the jaAvs alters with age in some species. The one exception referred to 

 above is fortunately tlie interesting hamata, the hooked jaws of which are recognizable 

 even at 5'5 mm. total length ; in young serratodentata the younger (dorsal) jaws alone 

 are hooked, and more slightly so than in hamata. 



Sagitta serratodentata, Krohn. (PL 4. figs. 1-6.) 



Characters. — Head small ; body slender, pin-like like blpmictata, thickest about the 

 middle of its lengtli, tapering gradually forwards and backwards ; a marked neck, but 

 no collarette ; body firm, retaining its shape. Longitudinal muscles broad, but thin ; 

 lateral fields rather narrow ; no marked constriction at the septum. 



Anterior fin long, extending to ventral ganglion, widest near its posterior end. 

 Distance separating the anterior and posterior fins very short. Posterior fin long, 

 longer and wider than the anterior, extending to (or very nearly to) the vesicular 

 seminales ; about as much on body as on tail ; widest point about midway between 

 septum and vesicuJse seminales. Tail-fin truncate. 



Ventral ganglion of medium size, prominent. Corona ciliata long, sinuous, extending 

 from between the eyes to about halfway to the ventral ganglion. Jaws strongly 

 curved; the younger (dorsal) jaws sei'rated and slightly hooked at the tip *. Teeth of 



* For a detailed description, see Knimbach, Zool. Jahvb. Syst. sviii. (1903) 579. 



