FRESH-WATER CRUSTACEA OF THE UNITED STATES. 649 



one upon the third segment. In the absence of all knowledge of the 

 nature and use of these appendages, it seems useless to speculate on 

 their importance as distinctive characters. In a species of Pontoporeia 

 from the Gulf of Saint Lawrence, which I suppose to be the P. affinis of 

 Kroyer, there are no such appendages on any of the thoracic segments. 

 This fact, together with the variation noticed in the specimens from 

 Lake Superior, would seem to indicate that these appendages are not 

 of so much importance as might at first be supposed. 



This species was found in great abundance in the dredgiugs in Lake 

 Superior in 1871, and occurred in every haul from 4 to 1G9 fathoms. 

 It was also dredged by Mr. J. W. Milner in Lake Superior in 1872, in 

 CO fathoms off Outer Island. It is common in the stomach of the white- 

 fish from Lakes Superior and Michigan, and probably also from the lower 

 lakes. All the specimens dredged in Lake Superior were taken in 

 August and the early part of September, and none of the females were 

 oRrrying eggs during that time. Females carrying eggs were dredged 

 by Dr. Stimpson, in Lake Michigan, in 40 to 60 fathoms, off Eacine, 

 Wis., June 24, 1870, and with them the adult male form with long 

 antennulfe and antennte. This peculiar form of the adult male, corre- 

 sponding perfectly with the same form of the European species figured 

 and described by Dr. Sars, I have not been able to find among the 

 numerous specimens from Lake Superior. A single specimen of this 

 form of the male was, however, sent to me by Dr. Stimpson under the 

 manuscript name of Gammarus Soyi, while two specimens of the female 

 were sent as Ganvnarus brevistylis. These are undoubtedly the same 

 as the Gammarius Royi and brevistilus mentioned, without description, 

 by Dr. P. R. Hoy, {loc. cit.) 



PONTIPOREIA FILICORNIS, Sp. nov. 

 Gammarus filicornis Stimpson, MSS. 



Male. — Outline of the head very much as in P. affinis. Eyes about as 

 large as in that species, slightly elongated, black. Peduncle of the an- 

 tennula reaching nearly to the distal end of the penultimate segment of 

 the peduncle of the antenna, about as long as the head and the first 

 segment of the thorax together ; first segment large and thickened ; 

 second half as long as the first ; third slightly more than half as long 

 as the second. Flagellum greatly elongated and very slender, reaching 

 nearly to the tip of the abdomen, and composed of thirty-three seg- 

 ments, of which the proximal are longer than broad, while they increase 

 in length distally, until, near the tip, they are many times longer than 

 broad, and exceedingly slender. The upper side of the flagellum is 

 nearly naked, only the alternate segments being furnished with two 

 minute setse near the distal extremity, while the under side of each seg- 

 ment is armed distally with minute setse, and most of the segments 

 with one or several clavate (olifactory) papillae, and many of the seg- 

 ments have in addition a peculiar transparent, shallow, bell-shaped ap- 



