112 THE VOYAGE OF H.M.S. CHALLENGER. 



or concentric furrows ; anterior extremity rarely spinous, posterior sometimes armetl 

 with a spine at the lower angle. Muscle spots arranged in a transverse row of three or 

 four, with two detached (sometimes coalescent) spots in front. Hinges composed of two 

 crenulated crests on the left (occasionally the right) valve, which articulate with corre- 

 sponding depressions of the opposite valve. Anterior antennae very robust, mostly five- 

 jointed, and bearing strong spines, last joint narrow and elongated; posterior antennae 

 four-jointed, urticating setae long and slender, bi-articulate. Mandibles large and numer- 

 ously toothed ; palp three-jointed, and bearing a distinct branchial appendage. The right 

 foot of the first and second pairs in the male different from the rest, that of the first pair 

 very strong and prehensile ; of the second very feeble, the apical portion rudimentary and 

 destitute of a terminal claw. Eyes distinct. 



Certain species of this genus are amongst the most abundant of European Ostra- 

 coda, and several have been described from distant parts of the- world, while in the 

 Tertiary epoch the genus seems to have been at least equally abundant. The almost 

 complete absence of this group from the Challenger dredgings is, therefore, very remark- 

 able, nor do I see any reasonable way of accounting for it except on the supposition that 

 these animals prefer shallower waters than those to which the work of the Challenger 

 was almost exclusively confined. At any rate, the oiily example found amongst these 

 dredgings is — 



Cytheridea spinulosa, G. S. Brady (PL XXXIII. fig. 6, a-d). 



Cytheridea spiimlosa, Brady, Ann. and Mag. Nat. Hist, ser. 4, vol. ii. p. 182, pi. xiii. figs. 1-6. 



Carapace, seen from the side, subquadrangular, oblong, not much higher in front than 

 behind, height equal to rather more than half the length ; anterior extremity moderately 

 well rounded, posterior scarcely rounded, subtruneate ; dorsal margin sloping gently and 

 almost in a right line from before backwards, ventral straight ; seen from above, the outline 

 is subcuneiform, being widest at the posterior extremity, width and height nearly equal ; 

 the lateral margins converge gradually towards the front, which is wide, obtuse, and 

 scarcely pointed in the middle, hinder extremity subtruneate, convex, and mucronate in 

 the middle ; end view nearly circular. . Shell-surface beset Avith closely-set, large circular 

 pittings, fringed on the anterior and front of the inferior margin with numerous short 

 teeth, and below the middle of the posterior extremity with a smaller number (usually 

 six or eight) of larger and unequal teeth. Length, 1-4 5th of an inch ('54 mm.). 



Cytheridea spinidosa was found only in a dredging from a depth of 15 to 20 fathoms 

 at Amboyna, and in a sounding made in 420 fathoms (October 20, 1875, near Station 

 287). The type specimens were found at Mauritius. 



[PL XXXIII. fig. 6, a-d. a Carapace seen from left side, h from above, c from below, 

 d from front. Magnified 60 diameters.] 



