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



Tropiocaris, 1 n. gen. 



Carapace one-fourth the length of the animal ; anteriorly produced to a keel-shaped 

 rostrum that reaches a little beyond the frontal margin. 



Pleon laterally compressed and slightly carinated, with a tendency to be posteriorly 

 produced on the dorsal surface into sharp teeth. 



Telson long, narrow, and tapering. 



Ophthalmopoda pyriform. 



First pair of antennae having the peduncle short and supporting two flagella. 



Second pair of antennas carrying a tapering scaphocerite, furnished with a small 

 tooth on the external distal angle, and terminating in a long and slender flagellum. 



Oral appendages not examined. 



Second pair of gnathopoda long and slender. 



First and second pairs of pereiopoda chelate. Three following pairs terminating in 

 a long, smooth propodos and styliform dactylos, and the fifth has the propodos long, 

 armed with a row of short spines, which culminate towards the distal extremity, and 

 terminate in a short dactylos. 



Observations. — This genus in many of its parts approximates so nearly to Acanthe- 

 phyra and Notostomus that it can only be considered as a separate genus for the 

 convenience of classification. The three genera agree in the most essential points of 

 their structure, but differ in points that readily attract notice. 



In Notostomus the carapace is dorsally carinated and elevated, and the rostrum 

 produced to a sharp point that reaches to a greater or less extent beyond the peduncle 

 of the first pair of antennae, and the laterahjvalls of the carapace that cover the branchial 

 chambers are strengthened by several strongly marked carinas. 



In Acanthephyra the dorsal surface of the carapace is not elevated, and only 

 carinated anteriorly. The rostrum is longer than the peduncle of the first pair of 

 antennae, and is generally coarsely serrate with teeth that are not continued posteriorly 

 to the gastric region, and there are no carinas over the branchial regions. 



In Tropiocaris the carapace is not dorsally elevated, but strongly compressed 

 anteriorly to a deep ridge, at the extremity of which the rostrum projects to a point, 

 and from its base the inferior margin on each side diverges to the orbit, and forms a 

 surface that overhangs the metope or facial wall as a sort of pent-house or hood. There 

 is no carina on the branchial regions, and the posterior dorsal or cardiac region is smooth. 

 The pleon, as in the two preceding genera, is dorsally carinated and posteriorly projects 

 into tooth-like prolongations. 



The branchias are arranged in the same manner as in Acanthephyra, but the 



1 tjoV/j, a keel ; na^t;, a shrimp. 



