178 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



twice as long in proportion as that of L. productus, and is long and nar- 

 row, varying somewhat in width and in size. The median ridge and edge 

 are finely spinulose, the tip is well rounded ; caudal stylet nearly as 

 long as in L. productus ; labrum a little smaller than in L. productus. 

 The antennae are the same as in L. productus, and the first maxillepeds 

 and second maxillse do not difl'er essentially. 



From L. glacialis Kroyer, of Greenland, it differs in the longer, larger 

 carapace, eleven terminal segments being uncovered in L. glacialis. 

 The spines on the excavation are much smaller ; telson twice as long and 

 not subtriangular, and excavated at tip, as in L. glacialis; eyes larger; 

 interocular tubercle decidedly smaller; labrum smaller. The first max- 

 illse are much longer than in L. glacialis, in which the branches are very 

 short and the second lamellate division very small and ovate, compared 

 with the same part in L. productus and couesii. 



Length of an average specimen from head to end of telson, 20.2™™ ; 

 telson, 5™™; stylets, 15-19™™. 



This is the first occurrence of the genus in North America south of 

 the arctic circle. It was collected by Dr. Elliott Ooues, naturalist of the 

 United States Northern Boundary Commission. He writes me that 

 they " occurred in myriads in several small prairie pools, from a hundred 

 yards to a half mile or so wide, exactly on the boundary-line, 49° N., 

 just 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 wadingdepth, 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. 



\y' Lepidurus bilobatus, u. sp., 10, <J 3 ? (Fig. 17). — Male. — 

 \\.- — .>.' ■' Carapace broad and short ; as broad as long, measured 

 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 L. couesii, 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) segments 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. couesii, in- 

 cluding the five teeth on the edge of the segments as 

 Fig yi.-Lepidu- -^ell as the spines. There are about sixteen segments 



rus bilobatus, Fack., ^ ^ 



n. sp., male. bcyoud the posterior edgp of the carapace; in L. couesii, 



eight. On the dorsal side of the abdominal segments there are eight 

 spines on the hinder edge, while there are nine in L. couesii. The species 



