MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
37 
Crangonyx mucronattis Forbes. 
Crangonyx mueronalus Forbes, Bull. Illinois Mus. Nat. Hist., i, 6, Dec., 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 antenme, 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 antennae of the male are two-thirds to four-fifths 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 joints, 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 antenme 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. Right 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 
lamina 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 joints. 
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 beyond the tips of the third. The latter art) 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 antennae 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. 
