36 University of California Publications in Zoology [VoL 23 
Characters.—Rostrum longer than carapace, and tapering more or less evenly 
from the widest portion (which is about one-fourth as wide as the rostrum is long) 
to an acute tip; armed above with seven to eight teeth, one or two of which 
are behind the orbit; below with three teeth. Ocular peduncles short and stout; 
the ocellus lies between the cornea and the stalk. Antennal scale is shorter than 
the rostrum, with blade exceeding the spine. 
Dimensions.—Type: length 45 mm. 
Type Locality San Diego, California. 
Distribution—From San Diego, California, to Gulf of California (Rathbun). 
Bay of St. Elena, Ecuador (Nobili). 
Genus Palaemonetes Heller 
Rostrum prominently toothed above and below. Carapace furnished with 
antennal and branchiostegal spine, but without hepatic spine. Mandible without 
palp. 
Palaemonetes hiltoni sp. nov. 
Plate 12, figure 5 
Description.—Closely allied to P. kadiakensis Rathbun (1902, p. 903; 1904a, 
p. 30, fig. 9), from Alaska, and intermediate between it and P. vulgaris Say 
(1818, p. 248), of the Atlantic. 
It differs from both P. kadiakensis and P. vulgaris in the proportional length 
of the propodal and carpal joints of the first two pairs of legs and in the relative 
length of the sixth abdominal segment as compared to the fifth. The following 
table will suffice to show these differences in the three species mentioned above: 
Palaemonetes kadiakensis P. hiltoni P. vulgaris 
First pair of legs, 
PLOPOMUSs Canplis) sete eeaeeeceeeee 282520 io It gto) 
Second pair of legs, 
PLOPOCUS) + CanpuUs seen ee 1 ; 2.00 8 alo) 1 : 0.60 
MILO US ss) CAT DUS geen oeseweeterenctecescceeocecne i250 1Ssa1200 1: 0.88 
Abdomen, fifth segment : sixth .......... 1: 2.00 13 Ia Ig 30) 
Otherwise the description and figure of P. kadiakensis as given by Miss Rath- 
bun does very well for P. hiltoni. On the whole P. hiltoni is the stouter of the two 
with less elongate and attenuate legs and a relatively shorter and stouter sixth 
abdominal segment. 
Regarding the number of rostral teeth of P. hiltoni, as only four specimens have 
been seen, no positive statement can be made. Those examined all had nine teeth 
on the rostrum and an additional one on the carapace behind the orbit; beneath 
the number ranged from three in three of the specimens to four in the fourth one. 
In P. kadiakensis the count based on a large number of specimens ranges from 
six to ten teeth above, of which one or two are behind the orbit, and from two to 
three teeth below. 
Dimensions.—Holotype (Cat. No. 48991, U. 8. N. M.): length from tip of 
rostrum to end of telson 26 mm.; carapace and rostrum together 10.5 mm. The 
three paratypes are respectively 20, 21, and 24 mm. in length. 
Type Locality—San Pedro, California (Stout and Stafford coll.). 
