62 TWELFTH ANNUAL REPORT. 



The form is as in D. pellucida, but the spine is more slender and 

 directed upward. The head is shaped much as in D. vitrea in 

 the young, but is much less prominent. The older form has a 

 shorter and more slender spine (none were seen in the ultimate or 

 spineless stage). The head is more evenly rounded, but still well 

 crested. The abdomen is very slendtr and the anal teeth diminish 

 rapidly in size from below upward. The claws are very short and 

 armed down the whole length with fine bristles. The abdominal 

 processes are well united at the base in old specimens, so that the 

 second seems a small process of the first. The shell is very trans- 

 parent and the spine is longer than in any other Daphnid. 

 In a young specimen the spine was 1. mm., the body 0.7 mm., and 

 the head 0.4 mm. In this specimen the spine was slightly curved, 

 the head elongate with a slight ridge in front. Another individual 

 had the spine 1.1 mm. long, while the remainder of the animal was 

 1.3 mm. This specimen also had a knife-like hyaline ridge on the 

 crest, which was obliquely truncate in front; it also had numerous 

 summer embryos in the brood sac. The spine was perfectly straight 

 and but slightly inclined upward. Older individuals have a rounded 

 crest as figured and no ridge. The spine is relatively somewhat 

 shorter but much more slender. The characters which most clearly 

 distinguish this species are the well crested head, which in young 

 as well as sometimes older specimens has a median hyaline ridge, 

 the withdrawal of the eye from the margin and the very long spine. 

 It resembles D. galeata in earlier stages. It is very much like D. 

 Iffivis or, in other words, is in the group of D. hyalina; but the study 

 of a considerable number of specimens from different localities con- 

 vinces me that it can not be united with that species in any of its 

 varieties. This species has only been found in autumn, Sept. — 

 Nov., lake St. Croix and Richfield in Hennepin county. 



Section II. 



Pigment fleck wanting. Head crested. The small, hyaline spe- 

 cies constituting this section, elevated by Schoeiler to the rank of 

 a genus ( Hyalodaphnia) and by Sars to that of a subgenus (Cepha- 

 loxus), are chiefly residents of the deeper parts of our larger lakes. 

 These forms, from their rarity, have been little studied and it is 

 uncertain how far the assumed specific distinctions are valid. 



Two species are known in America and they are not confined to 

 large lakes. 



