of the West Coast of North America. 399 



Pef7'olisthes occidentalism Stimpson. 



Petrolisthes occidentalis, Stimpson, Ann. Lye. Nat. Hist. N. Y. vii. 

 p. 73. 



Stimpson says of this species that it is scarcely to be 

 distinguished from P. sexspinosus, Gibbes ; " but the carapax 

 is slightly broader, the spines less prominent and acute, and 

 the abdomen and feet more pubescent.^' 



As he adds that the examination of a large number of spe- 

 cimens is necessary to establish these differences with cer- 

 tainty, it is evident that he did not feel sure of the specific 

 distinctness of the form. 



The characters given in the synopsis at the commencement 

 of this article are taken from Gibbes 's description of P. sexspi- 

 nosus (Proc. Am. Assoc. 1850, p. 190). 



I have not, to my knowledge, yet seen this form. 



Petrolisthes armatus, Gibbes. 

 Petrolisthes armatus, Gibbes, Proc. Am. Assoc. 1850, p. 190. 



Among the miscellanea from Lower California I find two 

 specimens which I refer to this species. 



The front is sinuous, the central portion arched forward, no 

 preorbital spine ; postorbital tooth obtuse ; a little in the rear 

 of the latter an acute spine, from which a not very prominent 

 raised border runs backward around the carapax, which is 

 punctate posteriorly, but with short rugosities anteriorly and 

 on the margins. 



Meros of chelipeds with a spine in front. Carpus almost 

 three times as long as wide, armed with three large distant 

 spines in front, and ten small ones along its raised outer mar- 

 gin ; distal margin of carpus lobular ; manus with a raised 

 inner margin, the outer denticulate with a row of small spines, 

 largest in the central portion of the palm, and passing into 

 tubercles anteriorly and posteriorly; dactylus with a raised 

 upper border ; opposed edges of dactylus and pollex finely 

 serrated. Meros of second pair with five or six small spines 

 on anterior margin, that of third pair Avith six more prominent 

 spines, that of fourth pair with four spines. A prominent 

 spine at the posterior distal end of the meros of the second and 

 third pairs, but none on the fourth pair. A long slender 

 spine upon the posterior distal angle of the propodus of each 

 of the ambulatory feet. 



Ambulatory feet with long setae, especially upon the three 

 terminal joints, which show traces of bands of darker and 

 lighter tints — red and straw-colour in the specimen (in al 

 cohol). 



