46 TWELFTH ANNUAL REPORT. 



cient to identify the genus, and indeed to indicate that either S. 

 americanus or a related form is intended, but it is hardly compe- 

 tent to alter names the significance of which is quite clear. 



"Sides striate with numerous parallel minute oblique lines; hind 

 edge of the body with a prominent angle in the middle. Antennse 

 with four filaments on the upper and five or the lower branch. 

 Color white or red. Length 0.1; stagnant water in the forests of 

 the Southern States." 



Sp. 1. Simocephalus vetulus, Mueller. 



-Daphniaveiula, BAIRD, Herbick. 

 Daphnia sima* MUELLER, LaTKEILLE, BOSO, KAMDOHR, (illUlTHUISEN, Desmarest 



Lamarck, M. Edwards, Koch, Gmelin, Mainuel, Jurink, Lil- 



LJEBORG, LEYDIG. 



^mocephalus vetulus, SCHOEDLKR, V . E. Mueller.'Kuez, Weismann, Claus, Cutz, 

 Bikge. 



This commonest and one of the largest species is apparently dis- 

 tributed over the northern hemisphere and abounds in all the 

 more shallow lakes. The head is rounded in front and is not an- 

 gled between the prominence of the eye and the beak. The body 

 is very large and not abruptly angled above, the spine of the shell 

 being inconspicuous and high, so that the free posterior 

 edges of the shell lack little of equalling the greatest hight of 

 the shell. The shell is covered with minute dense striations which 

 spring from the free edges. The pigment fleck is elongated in old 

 specimens and the upper angle follows up beside the suture sepa- 

 rating the antennary basin from the rest of the shell of the head. 

 The antennules are ornamented with minute spines. At the lower 

 angle of the shell are three curved spines which differ from the 

 preceding filaments. The number of eggs which are produced 

 at once is truly immense. Under favorable circumstances this 

 species reaches a large size, falling little if any short of 3 mm. S. 

 vetulus lives, by preference, among the leaves of aquatic vegeta- 

 tion. With us this species seems to live in the smaller pools as 

 well as in lakes of some size. I am not able to see any difference 

 in this respect between the various species. 



Sp. 2. Simocephalus semilatus. Kcch. 



Daphnia seirulata, KoCH, LlEViN. FISCHER, LILL.JEBORG. 

 Simocephalus serrulalus, L'EY DIG, ScHOEDLrtR, P. E. MUELLER, KURZ. 



Head narrow, extending anteriorly into a sharp spiny angle in 

 front of the eye. Dorsal line of the shell abruptly angled or 

 -curved posteriorly, projecting to form a broad obtuse spine behind; 



