Thomson. — On Neiu Zealand Crustacea Auomura. 189 



peduncle directed backwards. External maxillipedes with the 

 ischium broad and meros provided with a prominent internal 

 lobe. Abdomen small, bent under the thorax, to which it is 

 closely applied ; females with two (or three) pairs of slender 

 uniramous ovigerous appendages on the 4th, 5th (and 3rd) 

 segments ; males with one pair of genital organs on 2nd seg- 

 ment. 



I. Basal joint of antennal peduncle short, partially 



concealed in the orbital cavity, not reaching 

 the superior margin of the carapace. 



a. Sides of rostrum entire, lateral margins of 



carapace with a single post-ocular spine, or 



smooth .. .. .. ..1. Petrolisthes. 



b. Sides of rostrum spinose, lateral margins of cara- 



pace spinose . . . . . . . . 2. Petrocheles. 



II. Basal joint of antennal peduncle formiug an acute 



and somewhat flattened projection excernal to 

 the orbit, and joined to the margin of the cara- 

 pace, second joint placed at some distance from 

 the orbit .. .. .. .. ..3. Porcellana. 



Genus 1. Petrolisthes, Stimpson. 



1858. Petrolisthes, Stimpson, Proc. Acad. Nat. Sci. Philad., 



p. 65. 

 1876. Petrolisthes, Miers, Catal. N.Z. Crust., p. 59. 

 1882. Petrolisthes, Haswell, Catal. Austral. Crust., p. 145. 

 1888. Petrolisthes, Henderson, Eep. Anom. Chall. Exped., 



p. 104. 



Carapace subovate, depressed, usually slightly longer than 

 broad ; front triangular, with the sides entire ; lateral margins 

 more or less undulated, not spinose. Eyes rather large. 

 Chelipedes broad and flattened. Ambulatory legs with short 

 robust dactyli, ending in a single claw. 



Sides of carapace entire, front quite entire .. 1. P. elongatus. 



Sides of carapace with a spine or small tooth, front 



with small spines . . . . . . . . 2. P. novcB-zelandics. 



1. Petrolisthes elongatus, M.-Edw. Plate XXI, fig. 8. 



1837. Porcellana elongata, M.-Edw., Hist. Nat. Crust., ii., 



p. 251. 

 1843. Porcellana elongata. White, Dieffenb. N.Z., ii., p. 265. 

 1874. Petrolisthes elongatus, Miers, Zool. "Erebus" and 



"Terror," Crust., p. 3, pi. iii., fig. 3. 

 1876. Petrolisthes elongatus, Miers, Catal. N.Z. Crust., p. 60. 



Carapace nearly smooth, covered with fine granulations 

 and rather convex, rotundate in form, with thin entire lateral 

 margins, which end in a subacute tooth outside the eyes ; 

 front triangular, entire, depressed, with a median groove, apex 

 subacute or obtuse. 



