318 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



on the west bank of Frenchman's Eiver, Montana. You will not find 

 this stream on the map, perhaps, by this name. 



" It is one of the first of the whole series of similar streams flowing south 

 into Milk Eiver. The species was not observed elsewhere. The ponds 

 were extensive shallow sheets of sweet water, of a comfortable wading- 

 depth, generally with a little open space in the deepest part, but mostly 

 choked with luxuriant vegetation {Graminece, Utricularia, &c.). Date 

 of collection, first week in July, 1874." Thirty-two males and thirty-one 

 females were obtained by Dr. Coues : this equality in the number of the 

 sexes is noteworthy. 



Several females with eggs were also obtained by C. Carrington, of Hay- 

 den's U. S. G-eological Survey, at Smithfleld, Cache Valley, Utah. The 

 specimens are in the Museum of the Academy of Natural Sciences, 

 Philadelphia, to the curator of which I am indebted for the opportunity 

 of examining the specimens. 



Lepidurus bilobatus Packard. 



Plates XV, fig. 3; XVII, figs. 4,6; XXI, fig. 3. 



Lepidurus hilohatus Pack., Bull. U. S. Geol. & Geogr. Survey, F. V. Hayden, in charge, 

 ill, No. 1, 178, Fig. 17, April 9, 1877. 



10 (? , 3 ? . — Male. — Carapace broad and shorty as broad as long, meas- 

 ured along the median line. The eyes as in L. couesii. The excavation 

 in the front edge of the carapace is much larger and broader than in i. 

 muesii, and the teeth are more numerous, but very unequal in size, there 

 being a few large teeth, with a number of smaller ones between them. 

 The abdomen is longer than usual, with six (and part of another) seg- 

 ments beyond the last pair of feet, while in L. couesii there are only five. 

 The spines on the edges of the abdominal segments are larger than in 

 L. coue-^ii, including the five teeth on the edge of the segments as well 

 as the spines. There are about sixteen segments beyond the posterior 

 edge of the carapace ; in L. couesii, eight. On the dorsal side of the ab- 

 domin^il segments there are eight spines on the hinder edge, while there 

 are nine in L. couesii. The species differs from any others in the re- 

 markably short telson, which is short and broad, nearly one-half as long 

 ill proportion as in L. couesii. The segment is broader at base and the 

 telson is broader than in any other species; it is truncate at the end, 

 and divided by a slight incision into two well-marked lobes, with about 

 seven more or less well marked median spines on the blade of the tel- 

 son; this segment, including the telson, is as long as the preceding seg- 

 ments collectively. In the carapace, seen from beneath, the distance 

 from the anterior edge of the hypostoma to the anterior edge of the 

 carapace is much less than in L. coiiesH, while the hypostoma itself is 

 much more convex. The 1st pair of legs are much longer and broader 

 than in L. couesii, and the succeeding pair ai'e rather broader than in 

 that species. 



Length of body, including caudal stylets, 48™™ ; length of carapace 

 (measured along median line), 18™™; breadth, 18™™; caudal appendages, 

 ITi^™™; 1st pair of feet, 15™™. • 



Female. — Differs from the male in the much shorter body and shorter 

 first pair of feet. There are five segments beyond the last pair of feet, 

 and twelve segments beyond the edge of the carapace. It is easilj' dis- 

 tinguishable by the shorter abdomen and 1st pair of feet, but other- 

 wise it does not differ, the telson and caudal filaments being of the same 

 proportion. The egg- sacs were empty; they are situated on the tenth 



