216 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus 9. Hetcromysis, Smitli, 1874. 



Heteromysis, Smith, Report upon the Invertebrate Animals of Vineyard Sound and adjacent water?. 

 Clilvomysi's, G. O. Sars, Middelhavets IMj'sider. 



Generic Characters. — Form of body comparatively short. Carapace emaroinatc 

 posteriorl3^ not covering completely the trunk, frontal margin projecting in the middle. 

 Eyes small. Antennal scale very minute, lamelliform, setose on both edges. First pair 

 of true legs much stronger than the rest, with propodal joint entire and spinous at inner 

 edge ; terminal joint unguiform. Remaining legs feeble in structure, with terminal j)art 

 multiarticulate and setous, terminal claw obsolete. Caudal limbs in both sexes of same 

 structure, forming small, simple, non-articulate, setose plates. Telson comparatively 

 short, deeply cleft at apex. Inner plate of uropoda shorter than outer. 



Jiemarks. — This genus, first established by Professor Smith, is most prominently 

 characterised by the peculiar and strong development of the first pair of true legs, as 

 also by the caudal limbs in the male being of the same rudimentary appearance as in the 

 female. Three species of this genus have hitherto been recorded, viz., Heteromysis 

 formosa, Smith, from the eastern coast of North America, Heteromysis microps, G. 0. 

 Sars, from the J\Iediterranean, and Heteromysis norvegica, G. 0. Sars, from the Norwegian 

 coast. A fourth species, to be described below, was also taken on the Challenger 

 Expedition. All the species are decidedly littoral in character, being never met with 

 either in the open sea, or at any considerable depth. 



57. Heteromysis hermudensis, n. sp. (PI. XXXVIII. figs. 1-7). 



Specific Characters. — Form uf body exceedingly short and thickset. Carapace 

 evenly arched above, frontal projection triangular. Last caudal segment not longer than 

 preceding. Eyes ovoid, cornea occupying about a third part of the eye, ocular pigment 

 dark. Antennal scale oblong-oval, about three times as long as Ijroad. Telson triangular, 

 lateral edges armed on either side in their outer part with about six denticles ; apical 

 incision occupying third part of length of telson, somewhat broad, only inner half 

 bordered with spinules ; terminal lobes narrow, with two unequal apical spines. Length, 

 G mm. 



RemarTcs. — This species would seem to be most nearl}- related to the Norwegian 

 form, Heteromysis norvegica, G. 0. Sars, from which, however, it may be readily 

 distinguished by its much inferior size and more thickset form. It also exhibits great 

 resemblance to Heteromysis for m.osa. Smith, but diifers in the small size of the antennal 

 scale and the somewhat deviating form and armature of the telson. From the Mediter- 

 ranean form, Heteromysis microps, G. 0. Sars, it is likewise distinguished by the form 

 and armature of the telson, as also by its more fully developed eyes. 



