302 THE VOYAGE OP H.M.S. CHALLENGER. 



orbital margin, the third is more distant, and behind the marginal line of the orbit. The 

 dorsal surface is horizontal, especially marked in the smaller specimen. 



The ophthalmi are well developed, not large, but situated on tolerably long and 

 slender ophthalmopoda. 



The chelae are long and slender, and the digital processes are longer than the rest of 

 the hand. 



The pleopoda are long, and similar to those of species in allied genera. 



The telson is laterally fringed with hairs, and armed with three, small, spine-like 

 teeth. 



This is a deep-sea species, having been obtained from a depth of more than two miles 

 in one case, and more than three in the other. 



Hemipenseus gracilis, n. sp. (PI. XLI V. fig. 2). 



Very like Hemi'penseus spinidorsalis, but without the dorsal tooth on the third 

 somite of the pleon. Telson scarcely half the length of the outer ramus of the rhipidura. 



Length, male, 50 mm. (2 in.) ; female, 50 mm. (2 in.). The female is the more 

 robust. 



Habitat.— Station 207, January 16, 1875; lat. 12° 21' N., long. 122° 15' E.; off 

 Tablas Island, Philippines; depth, 700 fathoms; bottom, blue mud; bottom temperature, 

 51°"6. Six specimens; two male, two female, and two young. 



This species bears so close a resemblance to Hemipenseus spinidorsalis, that I could 

 not discover any difference sufficiently important to determine specific distinction, except 

 the absence of the characteristic dorsal tooth on the third somite of the pleon. 



On comparing specimens of similar size side by side, it is seen that in Hemi- 

 penseus spinidorsalis the rostrum is scarcely shorter, and projects less in advance of the 

 eyes, and the eye in Hemipenseus gracilis is wider than the stalk, and black instead of 

 brown. 



All the appendages bear a close resemblance to one another ; the chelae are slender, 

 and the fingers longer than the palm. 



The ventral surface of the pereion varies somewhat, projecting forward in this species in 

 the form of a flat, broad-based and sharply pointed tooth, whereas in Hemipenseus spini- 

 dorsalis it is obtuse at the point, but the difference is not such as to se]3arate them specific- 

 ally; and certainly had there not been in the collection specimens of both males and 

 females of this species, I should have considered them as being probably only sexually 

 distinct. 



The habitats of the two, though not distant, differ much both in depth and in tem- 

 perature. 



