612 Dr, W. T. Caiman on 



LXVIII. — On Heteroeuma sarsi, Miers. 

 By W. T. Calman, D.Sc. 



(Published by permission of the Trustees of the British Museum.) 



[Plate X.] 



The genus Heteroeuma was established in 1879 by Mr. E.J. 

 Miers for a species of Cumacean from the Straits of Korea 

 to which he gave the name //. sarsi. Although some 

 details have since been added to the original description by 

 Dr. H. J. Hansen and by the present writer, certain characters 

 of the genus still remain obscure, and the discovery of 

 related forms renders it desirable to attempt a redescription 

 of the surviving co-types of Miers's species. 



Heteroeuma sarsi. (PI. X. figs. 1—13.) 



Heteroeuma sarsi, Miers, Proc. Zool. Soc. 1879, p. 58, pi. iii. fig. 3 ; 

 Stebbiug, Hist. Crustacea (Internat. Sci. Ser.), i893, p. 304 ; 

 Hansen, Isop., Cumaceen u. Stomatop. der Plankton-Exp. 1895, 

 p. 56; Caiman, Cumacea of 'Siboga' Exp. 1905, p. 8; Zimmer, 

 Cumaceen der deutschen Tiefsee-Exp. 1908, p. 165. 



Immature female. — Length of body 17 mm. (fig. 1). 



Carapace less than one-fourth of total length, its vertical 

 height a little less than, and its transverse width about equal 

 to, one-half of its length. There is a median dorsal crest, 

 anteriorly, which becomes doubled in the posterior half of the 

 carapace ; on either side of the crest is a shallow depression, 

 broad anteriorly, but contracting to a narrow groove poste- 

 riorly. The breadth of the ocular lobe is more than two- 

 thirds of its length, and it reaches almost, but not quite, to 

 the tip of the blunt pseudorostrum. The eye in some of the 

 specimens still shows traces of dark pigment. The antennal 

 notch is deep and angular and the antero-lateral angle is 

 bluntly pointed and does not extend quite so far as the tip of 

 the pseudorostrum. The surface of the carapace is quite 

 smooth and the lower edge is not serrated. 



The free thoracic somites are without ridges and the first is 

 only exposed dorsally, being overlapped at the sides by the 

 second; the posterior thoracic somites are without ventral 

 teeth. The abdominal somites have each a dorsal and a 

 dorso-lateral pair of ridges, but these are very faintly marked. 

 The last somite (fig. 11) has the posterior margin on the 

 dorsal side excavated, with a median tooth, so that the anal 

 valves when closed are visible from above. 



