TERTIARY DECAPOD CRUSTACEANS. 167 



Superfamily PAGURIDEA. 



Family PAGURTD^). 



Genus and species indeterminable. 



(Plate 9, Figures 6 and 7.) 



Material. Dactylus of left cheliped, from the Yaqui Valley at 

 Cercado de Mao (Bluff 3), Santo Domingo; lower Miocene; C. J. 

 Maury, collector; 1916. 



Description. The upper surface of the dactylus is rounded from side to 

 side, while the lower surface is narrower and flat and the inner surface oblique 

 and sinuous (from end to end) , the two surfaces separated by a line of tuber- 

 cles. Upper surface covered with unequal granules, except near the pre- 

 hensile edge; thick outer edge also granulate; a few granules on flat surface; 

 oblique surface smooth. Eight prehensile teeth with brown tips; a shallow 

 sinus near proximal end of margin. Tip of finger broken off, but there is no 

 evidence that the finger is excavated at the tip. 



While this is a left dactylus, it is not clear whether it belongs to a 

 major or a minor cheliped. 



Genus PETROCHIRUS Stimpson, 1858. 



Petrochirus inequalis, new species. 



(Plate 9, Figures 13 to 15.) 



Type locality. The Amina River, Yaqui Valley, Santo Domingo; 

 lower Miocene; C. J. Maury, collector; May 22, 1916. 



Material. A pair of chelae partially embedded. Cat. No. 324467, 

 U. S. N. M. 



Description. The proximal end of both palms is lacking. The chelae are 

 very unequal, a similar cross-section of the palm of each showing that the 

 width of the palm is two-thirds as great in the smaller as in the larger chela, 

 while the inequality in the thickness of the two may be even more. Fingers 

 of large chela broad at base, tapering gradually toward the tips, excepting 

 that the dactylus has on its outer margin a sinus distad of the middle; measured 

 on the prehensile edge, the dactylus is over twice as long as basal width, 

 while the immovable finger is less than twice as long as basal width. The 

 tip of the dactylus folds under the immovable finger and is apparently not so 

 long. Fingers blunt-pointed. Most of the tubercles of the fingers are broken 

 off, leaving the tessellated background formed by their crowded, many-sided 

 bases. The tubercles which remain, especially those on the underside of the 

 palm, trend slightly distad, each surrounded anteriorly by a few small tuber- 

 cles, and the larger ones separated from one another by tubercles of medium 

 size. Tubercles conical, tip subacute, defined by a line from the basal portion 

 and easily broken off. 



The fingers of the small chela as they stand scarcely reach beyond the 

 proximal third of the large dactylus, but the chelae may not be in their true 

 relative position. The tubercles are similar to, but lower than, those of the 

 larger chela. 



Relationships. This species has a smaller left chela than any Petro- 

 chirus yet described. The fingers of the right chela are exceptionally 



