354 



GEOLOGICAL SUEVEY OF THE TEERITORIES. 



and bilobed, there being two short terminal tubes, with distinct, large 

 openings, directed downward. 



Female. — Second antennte large and long, extending back a little be- 

 yond the base of the ovisac, oar-like, expanding broadly on the outer 

 two-thirds, especially on the upper edge. The ovisac is subcorneal, the 

 base broad and concealed by the limbs ; it terminates at the posterior 

 edge of the fourth segment from the end, ending in two unequal flaps, 

 the upper four times larger than the under flap, and triangular in out- 

 line. 



Length of male, 23^™ ; female, 26 5^"™. Ellis, Kans., Dr. L. Watson, 

 collected June 26, 28, and 29, and again September 27, Octo- 

 ber 1, 10,, and 22, 1874, in pools of water on the plains, in 

 company with Esthcria and Limnetis. A fully-grown male 

 occurred September 27th. October 1-22 females of full size 

 were collected, in company with Apiis lucasmius, Estheria com- 

 j)leximanus, and Estheria mexicana.* The ovisacs still con- 

 tained eggs, though empty at the ends. 



!No striking variation was observed among several hundred 

 specimens of different ages. Dr. Watson writes that the gen- 

 eral color is pinkish, the 

 edge of the tail red, and 

 the genitals light blue. 



The sexual characters 

 are very distinct when 

 the animal is one-third 

 grown, the oviducts 

 being red with eggs, 

 and the males with the 

 frontal bush-like appen- 

 dage well developed. 

 The following account 

 the occurrence in 

 Kansas of this interest- 

 ing genus, and of Apus lucasanus, Streptocephalus texanus, Estheria 

 mexicana, and Limnetis I extract from a letter of Dr. Watson, dated 

 Ellis, Kans., October 12, 1874: 



The Apus moves about on the bottom of the pools, rarely rising enough 

 to allow the slipping of the net under him, and is not easily captured 

 unless in close quarters. The Estheria and Limnetis swim about, go- 

 ing to the bottom and coming to the surface, and are easily captured by 

 slipping a net under them when up. The Thamnocephalus are always 

 in medio, and by gentle action are easily taken. The forked-tail ones 

 (Streptocephalus) at the edge of the pool, and the larger emarginated- 

 tailed ones always in the middle, or in circumscribed clear places having 

 6 or 12 inches of water. The heavy rain of June 14 washed out the 

 xavines by torrents. The dates 1 have before given for former collections 

 indicate the development of those specimens after that date. Those 

 now sent (October 14) have developed, certainly since September 2; 

 probably since September 8; possibly since September 13. 



^''In relation to the localities where I have found the Crustaceans : 

 •'There are "divides" upon these plains, between streams; just here, 



* From Mr. R. P. WTiitfield we have received specimens of Estheria mexicana collected 

 \>j Dr. C. A. White, on the Vermilion River, Colorado, in company with Lepidurus 

 hilobatus Pack. See American Naturalist, xiv, 53, 1880, where this species is referred to 

 nuder the name of Estheria ivataoni Pack, (uo description), which is synonymous with 

 E. mexicana. 



Fig. 23. — Thamnocephalus platyurus Pack., malp, natural size, ^ 

 doi'sal and side view ; a head, and b end of body of female, showing 01 

 ovisac. 



