series of similar observations from different latitudes would be necessary before this could be 

 regarded as even probable. 



It seemed at first sight possible that in these Indo-Pacific serratodcntata might be found 

 an instance of the faster rate of life which has been alleged to characterise tropical plankton, 

 as the result of more rapid metabolism at higher temperatures; that these specimens might 

 prove not only to reach a higher complement of teeth, but also to attain sexual maturity at 

 a shorter total length than their Atlantic brethren. But the examination of a number of specimens 

 from both localities showed that the first evidences of sexuality appeared in both sets at about 

 the same total length of 9 — 11 mm. (it varies a good deal with the individual); it may have 

 proceeded a little more rapidly in the case of the tropical specimens, but there seemed to be at 

 most only the difference of a millimetre of total length on the average, in specimens at the same 

 apparent stage of sexual development. This is by no means definite enough to found a case upon. 



In young Krohnia hamata from the Siboga Expedition more teeth were observed than 

 in the corresponding specimens from the Faeroe Channel, but the question of sexual maturity 

 could not be well studied owing to the imperfect preservation of the former material. 



In summary it may therefore be said that at present there is a lack of positive evidence 

 to prove that European specimens develop fewer teeth than Indo-Pacific at the same total 

 leno-th ; and that although such a difference clearly existed between serratodentata from the 

 Bay of Biscay and from the area of the Siboga expedition, still it is practically certain from 

 Krohn's observations at Messina that this is not the expression of a mere difference of longitude, 

 but must be capable of some other explanation. 



At the same time, it need hardly be pointed out that a case of such wide variation 

 suo-aests that in the future, when more is known of the group, the number of species may be 

 considerably reduced. 



C. NOTES ON SOME SPECIES NOT CAPTURED BY THE SIBOGA EXPEDITION. 



Sagitta arctica Aurivillius. 



C. W. S. Aurivillius. Das Plankton der Baffins Bay und Davis' Strait. Festskrift Wilhelm 

 Lilljeborg, p. 188. Upsala 1896. 4to. 

 ? elegans Verrill. 

 A. E. VERRILL. Invertebrate Animals of Vineyard Sound and the adjacent water. United 

 States Commission of Fish and Fisheries. Part I, pp. 440, 453, 626. (For the years 1871, 

 1872; published 1873). 

 ? falcidetis Leidy. 

 J. LEIDY. On Sagitta, etc. Proceedings of the Academy of Natural Sciences of Philadelphia. 

 Year 1882, p. 102. 

 The original diagnosis of this form is too brief to enable any one but its describer to 

 identify it with certainty; it runs as follows: "Flossen wie bei S. hexaptera d'Orb. Greifhaken 

 11 (12), Vorderzahne 6 (7), Hinterzahne 15 (16), Schwanz-Segment (ohne Flosse) = \ des 

 Rumpfes. Korperlange 28 — 30 mm.". No figure of the species has been published, so far as 

 I can ascertain. 



