200 



DEPARTMENT OF THE NAVAL SERVICE 



The submature female of this species, 3.6 mm. in length, with the adult segmen- 

 tation but not having attained the full size and maturity, differs in several points from 

 the full-grown female. The genital segment (fig. 24) has a proximal protuberance in 

 place of the distal process (compare fig. 17 C) and does not possess the serrations at 

 the posterior lateral margin. In the full-grown form the second abdominal segment 

 has a fringe of shorter spinules at the lower margin. In the submature individual 

 while the fifth feet have the typical formation, the postero-lateral angle of the fore- 

 body is bluntly rounded instead of acuminate. 



Fig. 24. — Same. Part of forebody and the urosome of a submature female. 



13. Centropages hamatus. — This is a typical member of the microcalanoid plankton 

 whose distribution is to a large extent parallel with that of Tortanus discaudatus but 

 on the average it does not reach so near the shore line and extends further out to sea, 

 that is to say, over greater depths. This may be gathered in a general way from the 

 tables and it will suifice here to mention a typical example of a copious and clean, 

 gray-toned microcalanoid plankton, namely, the Souris Tortanus plankton exemplified 

 in No. 33 station 7. In addition to the proceeds of this station, Dr. Huntsman on 

 several occasions procured samples from canoes and motor boat«, thus establishing the 

 character of the Souris summer copepod plankton. Figure 25 shows the urosome of a 

 submature female with the adult urosome forming within the adolescent cuticle. It 

 was taken at the surface at Acadia station 62 on July 25. 



Fig. 25. — Centropages hamatus Urosome of adolescent 

 female, shortly before an exuviation, 



