178 N'oies on North American Crustacea. 



longitudinal rows of sharp tubercles, three in each row. The 

 basal joint of the external antennae is exposed from above, and 

 separated from the fronto-orbitar region by a deep suture or 

 pit, and there is also a deep pit on the spine of its exterior 

 angle, which spine is beneath separated from the rest of 

 the joint by a deep groove continuous with the superior pitted 

 suture ; beneath, also, the basal joint is channelled along its 

 external margin, where it forms the lower floor of the orbit. The 

 moveable part of the external antennae is shorter and broader than 

 in T. erosa^ and ciliated on both sides; the third and fourth joints 

 are broad and pitted, the fifth and terminal ones very slender. 

 The meros-joint of the endognath in the external maxillipeds, 

 is more prominent and less rounded at its external angle. In 

 the chelipeds the tips of the fingers are excavated, and the 

 tooth of the dactylus is not bifurcated. Meros of ambulatory 

 feet deeply bi-sulcated longitudinally, and armed with a series 

 of short strong spines along the superior margin. 



Length nine-tenths of an inch. 



Found at Cape St. Lucas, Lower California, by John Xantus, 

 Esq., tidal observer for the U. S. Coast Survey. 



It is difiicult to decide, without comparison of specimens, 

 whether this species be identical with T. erosa or not. We 

 have named it because we consider it far better for the interest 

 of science to admit a slight risk of adding a synonym, than to 

 refer a species to a locality at which it does not exist, which 

 would tend to confuse our ideas upon geographical distribution, 

 a knowledge of which constitutes one of the most important 

 aims in our investigation of species. 



Tlioe piiella, nov. sp, 



Carapax as in T. erosa protuberant, but broader at the 

 eyes, and with the antero-lateral sides straight or even a little 

 concave. Two protuberances on the intestinal region, and two 

 longitudinal ridges on the frontal. Eostrum acute, deeply 



