610 GEOLOGICAL SURVEY OF THE TEREITOEIES. 



the palmary margin is without the lamellar edge and without spines, 

 except two or three small ones at the tip of the closed dactylus. The 

 palmary margin of the second pair, in the male (Fig. 14), is only a little 

 oblique, is convex in the middle, has a broader lamellar edge than in 

 the first pair, and is armed on the outside with one, or very rarely two, 

 loDg, stout, and obtuse spines near the middle, and with two, three, or 

 very rarely four, successively smaller ones near the tip of the closed 

 dactylus. There are also two or three still smaller obtuse spines on the 

 inner side of the palmary margin near the tip of the dactylus. In the 

 female, the palmary margin of the propodus in the second pair of legs 

 is without the lamellar edge and the spines in the middle, and is straight 

 and nearly transverse. 

 The name lacustris is preoccupied. 



Gammaeus eobustus, sp. nov. (Plate II, Figs. 7-12.) 



Eyes small, nearly round, about equal in diameter to the thickness 

 of the proximal segment of the peduncle of the antennula. Antennula 

 much longer than the antenna; second and third segments of the 

 peduncle together but little longer than the first; flagellum about twice 

 as long as the peduncle, and composed of twenty-fiv^e to thirty segments 

 in fully grown males, and of twenty to twenty-five in the females ; sec- 

 ondary flagellum short, composed of three segments, of which the 

 terminal one is very small. Peduncle of the antenna long and stout; 

 the ultimate and penultimate segments subequal in length, and each 

 but little shorter than the flagellum ; flagellum (Fig. 8) stout, composed 

 of eight to eleven segments, and in nearly all adult specimens having 

 several of the segments furnished on the upper side with peculiar cup- 

 shaped appendages. First pair of thoracic legs in the male (Fig. 9) 

 with the propodus short and stout ; the palmary margin very oblique, 

 nearly straight, with a very narrow lamellar edge, and armed on the 

 outside with three large obtuse spines, and on the inside with quite a 

 number of small ones. In the second pair of legs (Fig. 10), the pro- 

 podus is very broad and stout, the palmary margin slightly oblique, 

 sinuous in outline, with a much broader lamellar edge than in the first 

 pair, and armed on the outside with a stout spine near the middle, and 

 two or three smaller ones near the posterior margin, and on the inside 

 with two or three small teeth near the posterior margin. In the female, 

 the first and second thoracic legs are much smaller and slenderer than in 

 the male. In the first pair (Fig. 11), the palmary margin of the pro- 

 podus is less oblique than in the male, slightly convex in outline, with 

 a prominent lamellar edge, but without spines except near the posterior 

 margin, which is itself armed with several small spines partially 

 obscured by numerous hairs. In the second pair (Fig. 12), the propodus 

 is proportionally much narrower than in the male, and has the palmary 

 margin very slightly oblique, quite convex in outline, with a broad 

 lamellar edge, and armed with two or three small spines near the poste- 

 rior margin, but without any median spine. 



Second and third segments of the abdomen with the infero-lateral 

 angles acute. In all the specimens examined, there are four dorsal 

 spines upon the fourth segment of the abdomen, two median and one 

 lateral each side; six upon the fifth segment, two median and two lateral 

 each side ; and upon the sixth, a lateral each side and no median. The 

 number of these spines is, however, very likely subject to some variation 

 as in the G. Umnceus. Outer ramus of the posterior caudal stylets about 

 five times as long as broad, and with only a few and small marginal 

 spines ; the terminal segment short and stout. Inner ramus consider- 



