[13] LAKE SUPERIOR ENTOMOSTRACA. 713 



Daphnia retrocurva Forltos, var. intexta. 



This form, although remarkably constant in the collections made in 

 northern Michigan, both from Lake Michigan and the smaller lakes, 

 differs from retrocurva* previously described, only in the inferior de- 

 velopment of the head and the smaller size and number of the pectina- 

 tions of the caudal claw. It is probably to be regarded as a slightly 

 depauperate form of retrocurva. 



The head, averaging two fifths the length of the body without the 

 spine, is helmeted, triangular, the apex antero-dorsal, recurved. Its 

 dorsal outline otherwise nearly straight or slightly concave • lower mar- 

 gin sometimes slightly sinuate near tbc rostrum, the latter produced 

 to or beyond the tips of the sensory hairs. Length of the borders of 

 the head subequal,but the antero-ventral margin commonly the longest. 

 Pigment speck wanting. Eyes small, about half as far from lower as 

 from upper margin of the head, and cither equidistant from rostrum 

 and apex, or a little nearer the former. Viewed from above, the head 

 is about half as thick at base as it is long. 



Dorsal outline of the body more or less convex, spine in the adult 

 nearly or quite equal to the depth of the valves. The latter about three 

 fourths as deep as long, surface conspicuously reticulate, lower margin 

 very slightly spinose, with sparse, short appressed teeth, which are con- 

 tinued on to the terminal spine. Dorsal abdominal processes quite dis- 

 tinct at base, brood cavity with one or two eggs. The caudal claws bear 

 a row of conspicuous teeth on the basal half, about twelve in number, 

 in two sets, those of the distal set the larger. (In retrocurva these teeth 

 are about twenty in number, the smaller proximal set twelve to fourteen, 

 and the distal more conspicuous set, about eight in number.) Beyond 

 these a row of very fine hairs continued nearly to the tip of the claw. 

 Posterior outline of the post-abdomen regular, bearing nine or ten 

 curved spines. 



Total length, without spine, about l.G mm . 



This was the only Daphnia taken in the longshore collections in Lake 

 Superior and in Lake Michigamme — the latter being, it will be remem- 

 bered, a body of water not directly connected with Lake Superior, but 

 emptying through the Menominee River into Lake Michigan. 



This form adds to the characters of the section Hyaloda/plinia the pec- 

 tinate claw of the group to which I), pulex belongs. It is distinguished 

 from D. pellucida at once by the armature of the claw and the lack of 

 the pigment speck* from cucullata and its varieties by the same char- 

 acters and by the fact that the dorsal abdominal processes are distinct 

 at base. From hyalina and galeata it is separated by the lack of the 

 pigment speck and the form of the head*. 



This Daphnia stood next in abundance in my Lake Superior collec- 

 tions to Cyclops thomasi, Diaptomus, and Epischura, occurring in large 

 or moderate number in every haul. 



# American Naturalist, XVI (1882), p. 642. 



