132 PROCEEDINGS OF THE NATIONAL MUSEUM vol. io5 



exhibited by Calvert mandibles. Although the alveolae were more 

 widely spaced, the teeth were somewhat smaller in size since 10 

 alveolae in the left mandible occupy an interval of 114 mm. 



The mandible from the shell marl (Falun) of Helvetian age at Salles, 

 Gironde Department, France, referred to Champs odelphis dationum 

 by Gervais (1859, pp. 305-306), is slightly smaller than that of this 

 Calvert specimen, since the height of the left mandible at the posterior 

 end of the symphysis is stated to be 28 mm. and at posterior alveola 

 35 mm. The illustration for this mandible (Gervais, 1859, pi. 83, 

 fig. 1) shows that the intervals between the alveolae were wider and 

 that the teeth were smaller — 12 alveolae were located in an interval 

 of 111 mm. 



PelodelphiSf new genus 



Diagnosis : Mandibles slender with elongated symphysis equivalent' 

 to less than one-half the length of each ramus when complete; sym- 

 physis ankylosed, tapering toward anterior extremity, approximately 

 U-shaped in cross section about half way of its length, and with 

 anterior half of its length bent upward; opposite free hinder portions ; 

 of mandibles form a blunt angle at level where they ankylose as ; 

 symphysis; probably 36 teeth in each mandible; 12 alveolae located 

 on each mandible posterior to hinder end of symphysis; 21 alveolae 

 located on preserved portion of left mandible anterior to posterior end 

 of symphysis; roots of teeth on symphysis implanted obliquely in 

 alveolae, which slope more backward than inward; anteroposterior 

 diameter of each of two alveolae at hinder end of symphysis in right 

 mandible, 9 mm.; transverse diameter of the same alveolae, 9 mm.; ; 

 diameters of anterior alveolae approximately 1 mm. smaller; opposite > 

 alveolae at hinder end of symphysis separated by an interval of 22.5 i 

 mm.; corresponding interval between 16tli alveolae (counting forward ' 

 from hindmost at posterior end of symphysis) is 5.5 mm. 



Pelodelphis gracilis, new species 



Plates 12-16 



Type specimen (USNM 13471): Ankylosed mandibles lacking 

 distal ends of both rami; hinder portion of right mandible incomplete. 

 Collectors, Remington Kellogg, C. Lewis Gazin, and Raymond M. 

 Gilmore, Aug. 11, 1933, 



Horizon and locality: In sandy clay of Zone 14 (about 18 inches 

 above contact with Zone 13), approximately 583 yards north of old 

 pier at end of Governor's Run Road (see U. S. Geol. Surv. Prince 

 Frederick Quad.), Calvert County, Md. Calvert formation, upper 

 Miocene. 



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