MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 37 



Crangonyx mucronatus Forbes. 



Grangonyx mucronatus Forbes, Bull. Illinois Mus. Nat. Hist., i, 6, Deo., 1876. Figs. 1 to 7. 



This remarkable species, remarks Mr. Forbes,* is perhaps entitled to rank as the type of a new 

 genus ; but , until I have the material for a more general study of its relations than I am able to 

 make at present, I prefer to place it with its nearest allies in the genus Crangonyx. 



Colorless ; blind ; length, 9 to 10 mm ; width, l mm . The head is a little longer than the first tho- 

 racic segment, its anterior margin concave at the bases of the upper antenna?, convex between 

 them ; the posterior margin straight in the middle and curving forward on the sides. The front 

 angles of the first thoracic segment are uncovered and produced a little forward ; the hind angles 

 of the first five segments are rounded and produced strongly backward. The first three abdominal 

 segments have the lateral margins and all the angles broadly rounded, and the posterior angles, 

 as well as the posterior margin of the seventh epimeron, are slightly notched and bristled. The 

 upper antenna? of the male are two-thirds to four-filths as long as the body. The first and second 

 joints of the pedicel are subequal, each about as long as the four basal joints of the flagellum ; the 

 third is one-third as long as the second. The flagellum is about five times the length of the 

 pedicel, and is composed of 30 to 35 joiuts, each with a few short hairs at tip, and all except the 

 seven or eight basal joints and the last with a slender olfactory club. The secondary flagellum 

 contains two bristled joints, together a little longer than the first of the primary flagellum. Pedicel 

 of lower antennae longer than that of upper, the last two joints equal, each a little longer than 

 basal joints of upper antenna. Flagellum nine or ten jointed, with olfactory clubs. Eight man- 

 dible with dental laminae; each, with five conical, obtuse, subequal teeth. The anterior lamina of 

 the left mandible is much the larger and stronger, with three very strong, blunt teeth; posterior 

 lamiua with three slender and acute teeth. Palpus, three-jointed ; basal quadrate about half as 

 long as second, which is clavate and nearly twice as wide as long, with about ten long hairs on its 

 rounded hind margin, which are longest and closest distally. Last joint a little longer and nar- 

 rower than second, regularly convex in front, straight on proximal half of hind margin, slightly 

 concave on distal half, and fringed here with about twenty-four slender hairs, the three or four at 

 tip becoming suddenly very much longer. A few scattered hairs on front margin of this joint. 



Inner plate of anterior maxilla is nearly hemispherical, about half as long as outer, with four 

 plumose hairs on the rounded margin, which are about as long as the plate itself. Palpus two- 

 jointed ; first quadrate, one-third as long as second, which is oval, pointed, tipped with two claws 

 and some smaller spines. Lamina? of basal joints of maxillipeds short, neither hair extending 

 beyond tips of succeeding joiuts. 



First two pairs of feet equal. Dactyl of first pair in male curved, two-thirds as long as hand. 

 The latter is broad-ovate, two-thirds as wide as long, the palmar and posterior margins forming a 

 wide angle. Long hairs on posterior surface in transverse rows. Palm with about fifteen short, 

 , notched spines, each with a hair arising from the notch. Carpus subtriangular, three-fourths as 

 wide as propodus, hind margin very short, with one or two pectinate spines and a few long hairs ; 

 second pair similar; propodus a little longer and narrower; carpus as wide as propodus, posterior 

 margin longer, with about five transverse rows of long bristles, of which the distal row are doubly 

 pectinate on terminal third. The three posterior pairs of thoracic legs increase in size backward, 

 the first of these being not quite two-thirds as long as the last. The seventh epimeron is narrow, 

 with the lower margin regularly arcuate. The tips of the first pair of anal legs extend beyond 

 the tips of the second, and these beyon d the tips of the thii d. The latter are therefore very short, 

 about as long as the pedicel of the second pair. The outer ramus is ovate, truncate, half as long 

 as the pedicel, and hairy at tip ; the inner is an unarmed rudiment, one-fourth or one-fifth the 

 length of the outer. The telson of the male is a smooth cylindrical appendage, usually about as 

 long as the first three abdominal segments, and as large as the last joint of the pedicel of the lower 

 antenna. It presents a very slight double curve, is obliquely rounded at the end, and tipped by a 

 cluster of short hairs. In some cases this appendage is half as long as the body. 



The female differs in the following particulars : The upper antenna? are only about half the 

 length of the body, the flagellum not more than three times as long as the pedicel, and the secondary 



* The following description is copied from Mr. S. A. Forbes' article. 



