igiQ-J •'^- Kemp : Notes on Crustacea Decaf^oda. 339 



Tympanomcrus stevcnsi, sp. nov. 

 Plate XIII, fig. 2. 



The carapace is transversely oblong; the anterior breadth is 

 about one and a half times the length and the depth about half 

 the breadth. The upper surface is slightly convex in both direc- 

 tions and is verv feebl}'' sculptured. A broad and inconspicuous 

 median furrow extends backwards from the base of the rostrum, 

 disappearing before it reaches the middle of the gastric region and 

 there is a shallow transverse depression oti either side some distance 

 behind the orbital border. The posterior limit of the gastric 

 region is defined by a well-marked transverse groove about one 

 third the breadth of the carapace. On the branchial regions there 

 are a few minute tubercles, bearing short setae, arranged in three 

 oblique rows. The two anterior rows are exceedingly short and 

 indistinct and fn^quently consist of only one or two tubercles each. 

 The most posterior of them is longer and more conspicuous; in 

 direction the row is as much longitudinal as transverse, and if it 

 were continued forwards the line so formed would pass through 

 the front. In this respect a marked difference exists between 

 T. sievensi and the closely allied T. f rater. Posteriorly the carapace 

 is traversed by a sharp and perfectly straight transverse ridge, 

 situated nearer the hinder margin than in T. stapletoni and T. 

 deschampsi. 



The front is obliquely deflexed and at the apex is broadly 

 rounded or with a very obtuse median point; its lateral borders 

 are slightly but distinctly constricted near the base. The breadth 

 of the front is only one eleventh or one twelfth the breadth of the 

 anterior border of the carapace and is thus much narrower than 

 in any other species of the genus. 



The orbits are very slightly oblique, much less so than in 

 T. pusillus, but not strictly transverse as in T. stapletoni. The 

 upper orbital border is microscopically beaded ; it is excavate near 

 the base of the front, but in its outer half is almost perfectly 

 straight. The lower border is a little sinuous in dorsal view and 

 is finely crenulate. On the floor of the orbit there is a crest that 

 extends throughout nearly the whole of its length ; it runs close to 

 the lower border and the space between the two is hollowed. The 

 outer orbital angle consists of a small acute tooth directed out- 

 wards. 



The lateral margins of the carapace are very slightly conver- 

 gent posteriorly and are straight, not convex ; the breadth of the 

 upper surface in the middle is thus a little less than its anterior 

 breadth. There is a small emargination or notch behind the outer 

 orbital angles and further back a series of minute denticles. 

 Throughout its length the margin is defined as a sharp crest 

 bearing short setae. At the extreme posterior end, as in T. pusillus, 

 it is bifurcated, one branch running to the margin at the base of 

 the penultimate legs, while the other — the more conspicuous of 



