502 Heterogenetic Development in Diaptomns.' [May, 



ScAPHOLEBERis ANGULATA, sp. nov. (Figs. 26-28, Plate V). 



The genus Scapholeberis at present consists of two species, 5". 

 nasiita Birge,-^ and vS. niiicronata with its three varieties (a)fronte 

 Icevi, (b)fronte cornuti of Europe, and (c) annata^ found in Min- 

 nesota, Illinois and Tennessee. With regard to the European 

 varieties it is remarkable that although they are not local varieties,^ 

 the horn upon the head appears in the larger individuals and not 

 as would be expected from the analogy of Daphnia, in young 

 and small individuals. However, it is to be noticed that the 

 spines of the valves in Scapholeberis are not persisting embryonic 

 characters like the spine in Daphnia, but the young are like 

 Ceriodaphnia. It may be that in like manner the crest upon the 

 head in Scapholeberis is, instead of an embryonic appendage as 

 in Daphnia. a later production. It might then be suggested that 

 Scapholeberis is now undergoing differentiation or, in other 

 words, is a new genus historically, while Daphnia is past the 

 acme of its activity in the direction in which it has differentiated, 

 and now retains its peculiarities by inheritance, and tends to con- 

 tinue them only so far as they are of functional value. 



The horn which sometimes appears in young of certain species 

 of Daphnia {D. galeatd) and seems so capricious in its produc- 

 tion, may be not unlike that of this species. 



Were it not that vS". mucronata is known to be very variable, it 

 might be admissible to create var. armata a new species. Addi- 

 tional details are given for this variety in Figs. 23-24, Plate vi. 



Scapholeberis angulata, sp. nov. — Head of medium size; rostrum directed down- 

 ward and backward ; eye of moderate size ; macula nigra indistinct; formices and 

 basin for antennee well developed ; antennules long curved, armed with two lateral 

 sense hairs as well as the terminal olfactory ? filaments; cephalic portion of the basin 

 of antennae marked by longitudinal lines connected at intervals by cross lines, infe- 

 rior portion of the part of the basin on the valves reticulate ; " mucro " absent, the 

 inferior posterior corner of shell simply sharply angled ; inner wall of shell furnished 

 with a row of small spines below and posteriorly for a part of the height of the 

 shell; caudal teeth 5-7 in adult, being more numerous than in any other known spe- 

 cies; size large. 



The " mucro " is absent in the smallest individuals seen. 

 Scapholeberis seems to lie between Daphnia and Ceriodaphnia, 

 agreeing with the former in being a divergent member of the fam- 

 ily, but -still with more affinities to the latter. Near Decatur, Ala. 



^Birge. Notes on Cladocera. 



^ Herrick. Notes on Crustacea of Minnesota, Geol, Rep, 1881, 



3 Kurz. Doclekas neuer Cladoceren, etc., p. 22. 



