REPORT «)N THE CRUSTACEA MACRURA. 71 



Tin' first somite is smooth, being, all but the elevated posterior margin, covered by the 

 margin of the carapace when extended. The second somite is also smooth except for the 

 central dorsal ridge and a deep sulcus traversing it from the boundary of the coxal plate 

 transversely To the median ridge. The other somites correspond, but posteriorly the 

 sulcus decreases and the smoothness is changed for a more tuberculated condition, which 

 on the posterior margin increases to a regularly crenated edge, which is conspicuous in 

 the fourth, fifth, and sixth somites. The lateral margins or coxal plates are tuberculated 

 on the dorsal surfaces, and the posterior edges are slightly crenated. The telson is 

 tolerably smooth and free from tuberculations; the anterior division is calcareous, the 

 posterior is membranous. 



The eyes are implanted in circular orbits fringed with small cilia. 



The first pair of antenna? is slender and longer than the second. 



The second pair of antennae has the terminal joint fringed with seven prominent cusps, 

 the smallest of which is on the inner margin, the others on the anterior. The penultimate 

 joint is small and narrow, while the next is broad and diagonally produced to a point that 

 projects on the outer side of the terminal joint and extends as far forwards as the extremity 

 of the most anterior cusp. . The prominent angle of the second joint is continuous with 

 a strong ridge that extends to the base and separates the joint into two divisions, the 

 outer of which is depressed, and has the margin fringed with four strong cusps. 



The first pair of pereiopoda is simple in form, short and robust. The three succeeding 

 pairs are sub-equal and moderately long, while the fifth pair is shorter, more slender, 

 and chelate in the female but simple in the male. 



The anterior pair of pleopoda has two branches broadly laminar in the female, 

 but long and narrow in the male. The second pair has one ramus, long, slender, and 

 three-jointed, the other short and foliaceous in the female, gradually decreasing in size in 

 each succeeding pair of appendages. In the male these same organs are little more than 

 rudimentary. 



Arctus im/maturus, n. sp. (PI. X. fig. 3). 



Carapace generally smooth, but showing slight indications of a central ridge with a 

 gastric projection. The cervical sulcus is obscure except where it deeply divides the 

 lateral and branchial ridges on either side. The lateral ridges are broken into a row of 

 narrow tubercles extending to the posterior margin of the carapace. A few imperfectly- 

 developed tubercles are faintly visible under a lens on the genital and cardiac regions. 



The pleon is smooth, with a slight central prominence, but without any arborescent 

 configuration of the dorsal surface. 



The eyes are implanted in circular orbits within the lateral margin, which is slightly 

 serrate from the anterior to near the posterior angle of the carapace. 



