1264 



CRUSTACEA. 



rior antennae also diverge from the Daphnia character, the branches 

 having uniformly three joints each, in the Daphnidae, and one or both 

 of the branches with less than this number in the Penilidae. 



M. E. Schodler, in his paper on the Acanthocercus rigidus, suggests 

 the subdivision of the Daphnioidea based on the number of legs, as a 

 natural grouping of the genera. 



The Lyncei are separated from the Daphnidae as a distinct family 

 by Dr. Baird : yet the species are identical in all proper family cha- 

 racteristics,— in the general form of body, in the number of organs, 

 their structure, and all points, except such as may be a basis for sub- 

 ordinate divisions. The only characters mentioned by Dr. Baird in 

 the characteristic of the family " Lynceidae" not included in that of 

 the " Daphniadae/' are, the existence of a black spot in front near the 

 eye j the convolution of the intestine ; and a distinct articulation at the 

 base of the abdomen. But the "black spot" according to Schodler, 

 exists hi most (if not all) of the Daphnidae : he has shown its con- 

 nexion with an opening in the basal portion of the anterior antennae, 

 and concludes that it is connected with the organ of hearing, being 

 probably the otolites. The convolution of the intestine is of little 

 importance as a basis for a family division. The genus Acantlwcercus, 

 for example, is closely similar to Baird's Macrotfirix, so closely that it 

 is referred to Macrothrix by Baird; and yet it has a convoluted intes- 

 tine, like the Lyncei. If this be right, the same genus may include 

 species of both kinds of intestine. 



The families of the tribe Daphnioidea, and the genera as yet known, 

 may be distinguished as follows : — 



Fam. I. PENILIDiE.* 



Pedes foliacei numero duodecim, angustiores. Antennae anticae obso- 

 lescentes. 



G. 1. SiDA, Straus j— Antennarum posticarum ramus longior 3-articulatus, alter 

 2-articulatus. Caput grande, infra non acute productum. Antennae lmas juxta 

 capitis basin insitae. 



* Dana, Proc. Amer. Acad. Sci., ii. 47, 1849; family Daphniadae, subfamily Siding 

 Dr. W. Baird, Brit. Entomost., 106; Sididae, Gray, Cat. Brit. Crust. Brit. Mus., W, 



| Sida, Straus, Mem. sur les Daphnia in M&n. du Mus. d'Hist. Nat, v., 38. 



