Notes on North American Crustacea. 227 



superior surface; distance between its anterior and posterior margins 

 much exceeding width of eye-peduncle. Front nearly three times as 

 wide at its anterior extremity as at its base between the eyes ; with a 

 supra-marginal crest interrupted at the middle. Inter-antennulary 

 septum or median process from epistome, armed with a strong sharp 

 tooth projecting forward. Chelipeds rather large, nearly smooth above; 

 meros broad, armed with three or four very small spines anteriorly : 

 carpus one-spined within, and with a crenulated outer margin indis- 

 tinctly one-toothed ; hands ornamented with slight longitudinal ridges 

 sparsely granulated or short-spinulated, also with two or three elongated 

 tubercles on inner side of palm, behind base of dactylus ; fingers much 

 compressed, not gaping, strongly toothed within, and with crenulated 

 exterior margins. Color of alcoholic specimen purplish. Length of 

 carapax in a female, 1.8 ; breadth, 2.8 inch. 



Found on the western coast of Central America, by Captain 

 J. M. Dow, of the Steamer " Guatemala," to whom we have 

 dedicated the species. 



CORYSTOIDEA. 



Pliosoina, nov. gen. 



Corpus rotundato-ovatum, longius quam latius, valde inflatum, Regio 

 faciei valde angustata, turaida. Frons vix rostrata, rostro fisso. Oculi 

 parvi, retractiles, longitudinaliter porrecti. Orbitae profundae, antrorsura 

 directae, angulo externo prominentes ; margine superiore unifisso. An- 

 tennae externae articulus basalis hiatum internum orbitae apte implens ; 

 pars mobilis mediocris, orbita exclusa, basi aperta. Antennulae in fossis. 

 Epistoraa brevissimum, fere obsoletum, apicibus maxillipedum tectum. 

 Maxillipedes externi elongati, eis Maioideorura plus minusve similes, 

 ischii apice interno antrorsum producto, palpo endarthroideo ; exognatho 

 magno, versus apicem contracto et dente intus armato. Chelipedes valde 

 debiles, parvi. Pedes ambulatorii primi paris longiores, extremitate 

 graciles, cylindrici ; tertii quartique paris versus extremitatem compressi 

 et ciliati ; quarti paris dactylus lanceolatus fere natatorius. Sternum 

 antice perlatum, retrorsum angustatum. 



