REPORT ON THE CRUSTACEA MACRURA. 65 



which widens out into a broad scale whose anterior margin is crenated in gradually 

 lessening degree as it approaches the anterolateral angle, where it becomes quite 

 smooth. This angle is prolonged forwards to an acute point, in a line with the 

 outer angle of the anterior margin of the carapace, from which the outer margin 

 recedes acutely backwards without any serration. The distal margin of the anterior 

 joint of the same antenna is armed with six teeth, which are widely separated except 

 thi' two inner, which are closer together. In the female these teeth are longer and 

 sharper than in the male. 



The antebrachial or cervical notch is broader than in Ibaccus incisus, and the 

 anterior angle of the carapace is narrower and sharper. Our specimens are all about 

 three inches and a half in length, whereas Ibaccus incisus is about five inches and 

 a half. 



The teeth on the margin of the carapace, inclusive of the anterior angle, are nine, of 

 which the posterior is small, and in one female specimen two others yet smaller are 

 visible. Another feature is that the lateral margin of the fifth somite of the pleon has a 

 posterior as w r ell as an anterior tooth or angle. Milne-Edwards in his description says 

 that the fourth joint (meros) of the " pates-machoires externes" (second pair of gnathopoda) 

 is armed with spines on the external margin. In our specimen I should call it serrate, 

 but this is also the condition of the ischium or the third joint on the inferior margin of 

 the inner side, as well as to a greater degree that of the outer margin of the first joint of 

 the basecphysis of the same appendage. 



On the dorsal surface in the median line is a slight elevation, scarcely worthy of 

 the designation of a crest, that terminates in a small point or tooth at the posterior 

 margin of the fifth somite. This species appears to be a form nearly allied to the 

 next genus. 



Themes, Leach. 



Thenus, Leach, Zool. Miscell. 



Scyllarus, Fabr., Suppl., p. 399; Latr., Hist. Nat. des Crust., t. vi. p. 81; Desmarest, Consid. 

 des Crust., p. 182. 



Geographical Distribution. — There appears to be only one species of this genus, and 

 that is recorded mostly from the Indian Seas. Sir Walter Elliot found it at Waltair, on 

 the Madras coast, Dr. Percival Wright at the Seychelles, and our small specimen was 

 taken in the Arafura Sea. 



There has been no record, so far as I am aware, of any species having been 

 found in a fossil condition nearer than Thenops scyllariformis, Bell, from the London 

 clay. 



(zool. CHALL. ESP. — PART HI. — 1886.) Eff 9 



