REPORT ON THE CRUSTACEA MACEURA. (551 



Pleou smooth ; third somite dorsally arcuate, sixth short, having the lateral margins 

 anteriorly confluent with the ventral surface. 



Telson long, narrow, tapering, laterally compressed and dorsally flattened, and subequal 

 in length with the outer plates of the rhipidura. 



Ophtlialmopoda biarticulate, standing at the extremities of a distinct somite. 

 Ophthalmus large, pear-shaped, projecting laterally, the posterior portion being furnished 

 with a large and well-formed ocellus, which, although close to, appears to be distinct from 

 the true ophthalmus, and as thickly facetted as the primary organ. 



First pair of antennas having the peduncle short, supporting two long, slender flagella 

 that are as long as the rostrum ; first joint excavate on the upper surface and armed on 

 the outer side with a sharp pointed stylocerite. 



Second pair of antennas carrying a long, narrow scaphocerite, armed on the outer side 

 with a small tooth, and a long and slender flagellum about the length of the animal. 



Mandibles furnished with a psalistoma and a three-jointed synaphipod. 



First pair of gnathopoda having the distal joints reflexed ; the basis armed with along 

 ecphysis, and the coxa with a small mastigobranchial plate and a small podobranchial plume. 



Second pair of gnathopoda long and pediform ; the basis carries a well-developed 

 ecphysis and the coxa a rudimentary mastigobranchia, but no podobranchial plume. 



First pair of pereiopoda slender and simple. Second pair long, slender and unequal, 

 the left being longer and more feeble than the right, and minutely chelate ; carpos 

 multiarticulate ; coxa supporting a rudimentary mastigobranchia, but no podobranchial 

 plume. Three posterior pairs of pereiopoda subequal, moderately robust, and terminating 

 in a small dactylos ; coxa of third and fourth pairs supporting a rudimentary mastigo- 

 branchia, but the fifth has none. 



Pleopoda biramose and semifoliaceous. Outer branch of the rhipidura furnished with 

 a well-defined diaeresis. 



Telson laterally compressed and subequal with the caudal plates. 



This genus is closely related to Plesionika, and, therefore, to Pandalus. In its 

 external features it is most easily determined by the character of the armature of the 

 dorsal crest, which consists of several spines that articulate in sockets, and several teeth 

 that are fixed and rigid, being part of the dermal wall. It forms a link between 

 Heterocarpus, A. Milne-Edwards, in which the armature of the crest consists entirely of 

 fixed teeth, and Pandalus, in which they are all spines. Another feature which is strongly 

 characteristic of this genus is the very perfect ocellus or secondary eye situated on the 

 posterior surface of the ophthalmopod, which, when the eye is lying at rest in the 

 excavation formed in the upper surface of the first joint of the first pair of antennas, is 

 vertically exposed. 



In Pandalus annulicornis the ocellus also exists, but it is not exposed beyond the 

 margin of the pigment that distinguishes the ophthalmus, but in Nothocaris it forms 



