MUSEUM OF COMPARA-TIVE ZOOLOGY. 155 



Family PORTUNID^. 



Achelous affinis, sp. nov. 



Carapace moderately convex both lon<,'itu(Iiiially and transversely, the frontal 

 region depressed, horizontal ; surface rugose, granular, and pubescent. Front 

 not prominent, composed of four blunt teeth, not counting the internal angle 

 of the orbit ; the two teeth near the median line are equilaterally triangular, 

 separated from one another by a triangular notch ; the next teeth on the outer 

 side are separated from those within by a shallow sinus, and fall off abruptly 

 on the outer side into a deep notch which separates the front from the inner 

 orbital angle. The two middle teeth of the front are a trifle longer than the 

 lateral teeth. The tooth formed by the projecting inner orbital angle does not 

 attain the level of the frontal teeth ; it is double, the orbital margin just out- 

 side of it being slightly folded, raised, and projected forward so as to form 

 a secondary tooth similar to that in A. spinimanus, but not so well marked. 

 The antero-lateral margin of the carapace is nine-toothed, including the tooth 

 at the outer orbital angle ; the posterior tooth is hardly larger than those in 

 front of it ; the posterior margin of these teeth is convex. The anterior edge 

 of the merus of the chelipeds is armed with five spines. The carpus has an 

 internal and a smaller external spine. There is a spine on the propodus at the 

 base at the point of articulation with the carpus, and another on the upper 

 margin a little distance back of the articulation with the dactylus. The distal 

 edge of the merus of the fifth pair of legs is spinulose. 



Length, 25 mm.; breadth, 39 mm.; length of merus of chelipeds, 24 mm.; 

 length of propodus, including digit, 33 mm. ; length of internal carpal spine, 

 measured from distal margin of carpus, 3.3 mm. 



Station 3379. 52 fathoms. 5 males, 4 females. 

 " 3390. 56 " 1 male. 



A large number were also taken in the tow-net at the surface at the follow- 

 ing stations: Oflf Mala Point; Hydr. 2627; Nos. 3355, 3371, 3382, 3386, 

 3398 ; 50 miles south of Guaymas. 



The specimens taken at the surface are small, and much darker in color than 

 those that came up in the trawl, but show no structural differences. I take 

 them to be the same species in the pelagic stage of its existence. 



This species is very closely related to Achelous depressifrons Stimps., from the 

 Atlantic side of the continent. Compared with J. depressifrons it is broader, 

 and the curve formed by the front and the antero-lateral margin of the carapace 

 forms an arc with a longer radius ; the lateral lobe of the front is broader ; the 

 tooth of the inner orbital angle is double, as above described; the teeth of the 

 antero-lateral margin have broader bases, and the anterior one at the outer 

 orbital angle is not so prominent; the protuberances on the cardiac and bran- 

 chial areas are less prominent; the internal carpal spine is shorter, and the 

 distal margin of the merus of the fifth pair of legs is denticulate behind the 

 articulation nf the carpus. 



