S. I. Smith on new Crustacea from N, America. 119 
ated midway between the rostrum and the outer angle; the 
orbits entire, slightly removed from the anterior margin and 
connected with it only by a suture. Antenne with the inner 
margins approximate, 
This genus is most nearly allied to Ibacus and Parribacus 
but is very distinct from both of them in the entire lateral mar- 
gin of the carapax, the closing of the orbits in front, and the 
form of the rostrum. 
Evibacus princeps, sp. nov. 
Whole upper surface verrucose and nearly naked ; five low, 
tuberculose elevations on the median line of the carapax, of 
which one is at the base of the rostrum, two on the gastric re- 
gion, one on the anterior part of the cardiac, and one on the 
posterior margin ; similar elevations on the middle of the sec- 
ond and third serments of the abdomen, and a very slight one 
on the fourth. Carapax strongly convex transversely ; the an- 
terior margin nearly straight, except at the lateral angle where 
itis slightly curved forward ; lateral margin strongly curved, 
with a broad notch at the cervical suture behind which the 
margin is very slightly, obtusely and irregularly toothed. An- 
tenne together as broad as the anterior part of the carapax ; 
the outer margins coarsely and irregularly serrate and their out- 
line forming the segment of a circle. Everywhere beneath 
naked and nearly smooth. External maxillipeds with the outer 
margin of the merus divided into a number of slender proces- 
ses, Legs so short that when bent forward in their natural 
position they are concealed beneath the expansions of the car- 
apax ; those of the first and second pairs with the superior 
angle of the merus raised into an obtuse crest; dactyli of all 
half as long as broad. Whole length of body, 14 in. ; length 
of carapax, including rostrum, 5°8 ; breadth of carapax, 7°9. 
A single female specimen of this remarkable species, the first 
of the Scyllaride discovered upon the west coast of America, 
was sent fot La Paz, Lower California, by Capt. Jas. Pedersen. 
Arctus Americanus, sp. Nov. 
Carapax as broad as long, median crest high, covered with 
low squamiform tubercles, tridentate, the anterior tooth small 
and situated half way between the front and the second tooth ; 
lateral crests very high, anterior portion with two teeth, above 
the eye and separated by a deep notch from the posterior por- 
