252 



ALLAN HANCOCK PACIFIC EXPEDITIONS 



VOL. 18 



At first, in my researches, it was believed that this species comprised 

 two distinct forms, employing the extremes in the following table : 



Uropods 1-2 



Peraeopod 5, 

 article 2 



Third epimeron 



Type A 

 Spines slender 



Very broad 



Lower margin well rounded 

 Teeth nearly obliterated 

 Lower margin serrate 

 Lower margin setose 



Posterior edge concave 

 Numerous setae 



TABLE 4 



Type B 

 Spines stout, short 



Narrower 



Lower margin truncated 



Teeth distinct 



Lower margin smooth 



Lower margin setulate 



Posterior edge straight 

 Few setae 



It was considered that these forms either represented ecological 

 subspecies or were determined by larger size and greater age of type A. 

 Intergradations between the two types have been encountered quite fre- 

 quently. These are specimens in which the differentiating criteria are 

 blended between the extremes or have one or more characters of the 

 second type associated with the rest of the criteria of the first type. Size 

 does appear to play a limited role; the greatly expanded second article of 

 peraeopod 5 and the concave third epimera generally are associated with 

 large specimens, although exceptions occur. 



Analyzing hundreds of specimens left the writer with the impression 

 that ecological conditions, perhaps the abundance of food, or the kind of 

 major community in which the animals exist, determine the size of the 

 oldest adults in a population. Attempts were made to correlate large 

 populations with some observable physical factor which had been recorded 

 at the time of collection but the data are too complex to be of use at this 

 time. It is hoped that correlations can be made when we understand the 

 community relationships and distributions better. 



PLATE 33 

 Paraphoxus obtusidens (Alderman), female, 13 mm, Sta. 2091-52. 



Figs. A,B, entire animal, dorsal and lateral. 

 Heads : 



Figs. C, female, 10 mm, Sta. 2348-53. 



D, male, 5 mm, San Quintin Bay, L. C. 



E, male, young, 6 mm, Sta. 1372-41. 



F, female, 8 mm, Sta. 478-35. 



G, female, 6 mm, Sta. 677-37. 

 H, female, 15 mm, Sta. 1140-40. 

 I, male, 7 mm Sta. 279-34. 



J, male, young, 5.5 mm, Sta. 1169-40. 



