NO. 1876. ON THE CRUSTACEAN ORDER CUMACEA—CALMAN. 



639 



Fig. 48.— Diasttus 

 bidentata, im- 



MATtlRE FEMALE, 

 THIRD LEG. 



ridges behind the ocular lobe are less pronounced. The pseudoros- 

 trum is longer and more acute than in the male of D. scorpioides. 

 The penultimate thoracic somite is produced backward dorsally as in 

 the female. The lateral processes of the last thoracic 

 somite are more produced than in the female, though 

 still blunt. 



There is a stout median ventral spine, followed by a 

 small tubercle, on the first abdominal somite, and two 

 median tubercles on the second. The telson is about 

 two and a half times as long as the last somite; the 

 distance fi'oni its base to the dorsal protuberance is 

 less than half that from the protuberance to the tip; 

 the lateral spines are longer and more numerous than 

 in the female. 



The antennal flagellum is about as long as the body. 

 The uropods, as usual, are much longer and more 

 slender than in the female, though the peduncle is 

 shorter than the telson, and have very numerous ser- 

 rate spines on the inner edges of peduncle and endopod. 



Young males, in wliich the pleopods are not furnished \\ith natatory 

 setae, resemble the females in general form and have a large lateral 

 spine on the carapace. 



Remarlcs. — This species has a considerable resemblance to D. dalli, 

 but it differs conspicuously in the large lateral teeth of the carapace. 

 There is a certain amount of variation in some 

 characters. A number of specimens from Point 

 Franklin (No. 7928, U.S.N.M.), the most northerly 

 locality from which the species has been obtained, 

 reach a much greater size than the holotype, 

 an ovigerous female having the carapace 4.75 mm. 

 in length, indicating a probable total body length 

 of about 16.5 mm. when complete. The carapace 

 is more inflated, the pseudorostrum more obtuse, 

 the ridges on the carapace less prominent, and the 

 tooth of the second ridge much more blunt than in 

 the typical form. On the other hand, specimens 

 from Albatross station 2841 (near Unalaska) of 

 about the average size, with the ridges of the 

 carapace relatively inconspicuous, have the tooth 

 very large and more acute than in the specimen 

 figured. 



Localities. — Near Point Belcher, Arctic Ocean; 9 fathoms; sand; 

 W. H. Dall; U.S.N.M. 13382. 



Ten miles west of Point Frankhn, Alaska; 13^ fathoms; sand; 

 Point Barrow Expedition, August 31, 1883; U.S.N.M. 7928; 10 

 females (very large). 



Fig. 49.— Diasttlis bi- 

 dentata, immatuee 

 female, last somite, 

 telson, and uropod. 



