ISOPODA. 53 



Family: STENETRIID.E * 

 Stenetrium, Haswell. 



1881, Stenetrium, Haswell, 'Pr. Linn. Soc. N.S. Wales,' vol. 5, p. 478. 



1882, Stenetrium, Haswell, 'Cat. of Australian (Malacostracan) Crustacea,' p. 308. 



1884, Stenetrium, Chilton, 'Trans. N. Zealand Instit.,' vol. 1G, p. 251. 



1885, Stenetrium, Haswell, 'Pr. Linn. Soc. N.S. Wales,' vol. 9, p. 1009. 



1886, Stenetrium, Beddakd, ' " Challenger " Isopoda, Reports,' vol. 17, pt. 48, p. 8. 

 1895, Stenetrium, Hansen, ' Isopoden der Plankton-Exp.,' p. 6. 



1902, Stenetrium, H. Richardson, 'Trans. Connect. Ac. Sci.,' vol. 11, p. 295. 

 1905, Stenetrium, Hansen, 'Proc. Zool. Soc. London,' pp. 303, 316. 



Five species have been assigned to this genus, S. armatum, Haswell, S. inerme, 

 Haswell, S. fractum, Chilton, S. haswelli, Beddard, and S. stebbingi, Richardson. 

 But Haswell's S. inerme differs from his other species in having rounded lateral 

 eyes, the antepenultimate joint of the maxillipeds distally narrowed, and perhaps, also 

 by having the rostrum subacute. It appears to belong to the genus Notasellus, 

 Pfeffer, 1887. The union of the other four species in a single genus is probably 

 justifiable, though in each case some important evidence is wanting. For S. armatum 

 Haswell has twice figured the mandible, and on each occasion gives no indication 

 of its possessing a molar. In S. haswelli, and in the species about to be described 

 from Ceylon, this part of the mandible is strongly developed and too conspicuous to 

 be overlooked. In the descriptions of S. fractum and S. stebbingi the presence or 

 absence of this structure, is not discussed. For the last-mentioned species no account 

 is given of the pleopods, and for the other species the accounts of these organs are 

 variable or uncertain. Including the new species, which is nearly allied to what is 

 known of S. fractum, the genus may be defined as follows : 



Body depressed, parallel-sided. Pleon consolidated. Head bluntly rostrate. Eyes 

 obliquely dorsal. First antennae short, inserted close to the rostrum on either side 

 of it. Second antennae elongate, with exopod on the third joint. Mandible with 

 palp. Maxillipeds with third to fifth joints broad, sixth and seventh narrow. First 

 gnathopods simply or complexly subchelate. Second gnathopods and all the 

 peraeopods slender, ambulatory, biunguiculate. Pleopods not in every case biramose. 

 Uropods biramose, not adjacent, inserted apically on the telsonic segment. 



The uncertainty attending the characters in some of the species makes it difficult to 



* After the manuscript of this paper had passed out of my hands, I received the luminous essay, " On 

 the Morphology and Classification of the Asellota-group of Crustaceans, with Descriptions of the Genus 

 SU a' triii in, IIasw., and its Species," by Dr. H. J. Hansen ('Proc. Zool. Soc. London,' p. 302, April 18, 

 1905). In this the new family Stenetriidse is defined (Joe. cit., p. 315), and nine species of Stenetrium are 

 described, with illustrative figures of several and a conspectus of them all. Five are new, S. rneditermneum, 

 S. serniliiin, S. occidmtale, S. antillense, S. siamense. For a more accurate account of the pleopods than I 

 had myself arrived at I am now indebted to Hansen's instructive treatise. 



