§3 



Palp of ext. maxillipeds articulating with outer angle of 

 anterior margin of merus i i 



2. Exognath of ext. maxillipeds broader than, or at least as 



broad as, ischium. Dactyli of legs not flattened ... 3 



Exognath of ext. maxillipeds narrower than ischium . . 4 



3. Carapace flat, depressed Ptychognathus Stimpson 



Carapace convex in both directions. Meropodites of walking 



legs with spines along postenor margin Pyxidognathus A. Milne-Edw. 



4. Lateral. margins of carapace entire, without teeth. Front 



about one-third wiclth of carapace. Ischium and merus 

 of ext. maxillipeds distinctly wider than long. Very small 



species Acmaeopleura Stimpson : ) 



Lateral margin of carapace clentate 5 



5. Breadth of carapace equal to of slightly less than length ; 



one obscure tooth behind ext. orbital angle. Merus of ext. 

 maxillipeds broader than long, scarcely auriculate. Legs 

 flattened, heavily fringed with hairs at outer margin. . Planes * Leach 3 ) 

 Carapace always wider than long 6 



6. Merus of ext. maxillipeds auriculate at distal outer angle 7 

 Merus of ext. maxillipeds not expanded at distal outer 



angle, nearly quadrate 9 



7. Propodites of walking legs cylindrical, dactyli styliform. . 8 

 Propodites of walking legs flattened, natatorial, as also are 



the dactyli. FYont horizontal, anterior margin perfectly 



straight Varuna H. Milne-Edwards 



8. Very aberrant species, Xanthoid-like ; lateral margins of 



carapace diverging considerably backward in their anterior 

 half, with two epibranchial teeth behind ext. orbital angle ; 

 the latter and the first epibranchial tooth serrulate at 

 outer margin aad separated by a very wide sinus. Merus 

 and ischium of ext. maxillipeds both wider than long (as 

 in Acmaeopleura) ; ischium shorter than merus ; suture 

 between them angular. Chelipeds of d" very bulky, much 



1) Pioc. Ac. Nat. Sc. Philadelphia, 185S, p. 105; Smithson. Inst., Miscell. Coll., v. 49, 1907, p. 130. The genus is founded 

 on A. parvula Stimpson (1. c, 1907, p. 130, pi. II, f. 4), found at Ousima, and recently Miss Rathbun added a second species, .-/. rotunda 

 (K. Dansk. Vid. Selsk. Ski., 7. Raekke, Afd. 5, n IJ 4, 1910, p. 327, textfig. 10) from the Gulf of Siam. 



2) Former authors have distinguished several species within this genus, but now it is generally believed, that there are only 

 two. The type species is Planes minutus (Linnc), that was originally referred to Caitcer by LlNNÉ and Herbst, to Grapsus by iLatreiu.e. 

 As is well known, this is the common and very variable Gulf Stream crab, occurring in great numbeis on the floating Sargassum, but 

 also on turtles. on floating timber etc. It has been met with in all the warmer seas but is essentially Atlantic. The second species is 

 Planes marinus Rathbun (Proc. U.S. Nat. Mus., v. -47, 1914, p. 120) from Lower California. 



Beu. (Hist. Brit. stalk-eyed Crust., 1S53, p. 134), KlNGSLEY (Proc. Ac. Nat. Sc. Philadelphia, 1SS0, p. 201—202, note) and 

 Stebbing (S. A. Crust., prt 5, 19 10, p. 320) all agree in stating that Planes is a manuscript name of Leach, and that it was first 

 published by BOWDICH in 182J (Exc. to Madeira and Porto Santo, p. 15, f. 2<;, li'). 



83 



