226 



BULLETIN" 57, UNITED STATES NATIONAL MUSEUM. 



Type-species. — Ristiotus maculatus J. A. Allen. 

 Geographic distribution. — Southwestern United States. 

 Number of forms. — The type species is the only member of the 

 genus thus far discovered. 

 Characters.- — Dental formula : 



2 3. 1. -2-4567.2-2 1-1 



2-2 



3-3 



=34. 



12 3. 1. -2-4567* 3-3' c l-l'^ 2-2' m 3-3 



Upper incisors alike in form, slender, with well- developed cingula, 

 and simple, styliform crowns, the outer somewhat larger than inner, 

 which is in contact or nearly so with canine ; lower incisors trifid, the 

 middle lobe largest, especially in i , and i ... Upper canine small and 

 weak, barely more than twice the height of inner incisor, which it 

 rather closely resembles in form; lower canine relatively smaller 



than in any other known Vespertilionine 

 bat, its crown scarcely higher than that of 

 pm i and not as high as protoconid of m x 

 or m 2 , with a noticeable posterior heel ris- 

 ing at edge to a distinct cusp, and a large 

 secondary cusp anteriorly rising above 

 crown of outer incisor, and giving the 

 tooth when viewed from the side and 

 slightly in front an unequally bilobed ap- 

 j>earance unique so far as I have seen in the 

 order. Anterior upper premolar minute, 

 scarcely more than one-third as large as 

 outer incisor and rising barely to cingulum 

 cf canine. It stands in the tooth row at 

 the middle of the narrow space between 

 canine and large premolar, and in form resembles the incisors, except 

 that the crown is relatively lower and thicker ; large premolar of the 

 usual form, but very deeply concave on anterior border; lower pre- 

 molars of the ordinary Vespertilionine type. Molars normal ; m * 

 and to 2 with barely indicated hypocone, and with protocone sepa- 

 rated from outer cusps by a rather unusually wide space, para- 

 cone and metacone high and slender, mesostyle rather short but W 

 pattern very distinct; to" with well-developed metacone and three 

 commissures, the area of its crown fully half that of either of the 

 other molars; lower molars with all the cusps unusually high and 

 slender, especially the protoconids, which considerably exceed the 

 hypoconids; a distinct though low cingulum cusp behind the ento- 

 conid in each tooth. Skull (fig. 37) with large, rounded, though 

 rather low brain case and excessively weak rostrum; zygomata 

 abruptly expanded at middle; audital bullae very large, and much 



Fig. 37. — Euderma maculatum 

 Adult male. Mesilla Park 

 New Mexico. No. 122545. xlj. 



