840 rROrEEDIN(;s of the XATIOXAL Mr,SEUM. VOL. XXX. 



The exact position in the Miocene to which Leptoplioca belongs is 

 a matter of much interest, and, fortunately, some lij;-ht is thrown on 

 that subject 1)}' the fossil shells found in the marl adhering to the tvpe- 

 specimen. These have been identified bv Dr. William H. Dall, who 

 kindly took them in hand at my request, as representing Yenux rileyi 

 and a species of Ci'ast:iateUit<^x. Reference to Prof. George B. Shat- 

 tuck's article on the Geological and Paleontological Relations of the 

 Maryland Miocene" shows that Venns rileyi and (^rds.safi/lHtcx ukII- 

 rni.H have been found together in the Calvert Clitfs only in zone 10, and 

 at a point 1 mile north of Plum Point; or, in other words, 2 or 3 miles 

 south of the point where the bones of Leptoijhoea were found. While 

 species of CrasKutellitex have been found in other zones of the Calvert 

 Clitfs, V<mus rileyi appears to occur onl}' in zone l<i. It seems highly 

 prol)ablo, therefore, that Leptoplioca belongs to this zone of the Cal- 

 vert formation. The Calvert formation represents the Lower Mio- 

 cene, a fa(.'t which is of interest because the majority of Van Beneden's 

 genera and species are assigned to the Pliocene. Onh' '^[onatherium 

 and Pt'ophoea are assigned to the Miocene, and even these to the 

 Upper rather than to the Lower Miocene. It is to be noted, however, 

 that the "sable noir" in which Prophoea occurs is associated by 

 Van Beneden. on the authority of Nyst. with the Miocene of the 

 Vienna Basin/' which formation Zittel places on the Middle ^Miocene.* 

 The Tertiary f)eds of Bessarabia, in which the remains of Nordmann's 

 Phoca maeoticd^ the nearest relative of Leptophdca loiix, were found, 

 are also assigned to the ^Middle Miocene. 



EXPLANATION OF PLATES. 

 Plate LXXV. 



Fig. 1. Right huineru.s of P/;oro (/j-ff/i/oNc/tca. Anterior view. 



2. Right humerus of Lejitophoca lenis. Cat. No. 5359, U.S.N.M. Vert. Paleon. 



Type. Anterior view. 



3. The same. Posterior view. 



4. The same. External view. 



(All the figures a little less than natural size.) 



Platk LXXVI. 



Fig. 1. Right radius of Liptoplmrd leu Ik/ Exterior \-iew. Cat. No. 5362. 



2. Proximal end of eonjoined til)ia and fibula of Liptophoca leni^f Anterior 



view. Cat. No. 536 L 



3. Posterior lumbar vertebra of Leptoplioca lenis/ Dorsal view. Cat. No. 5363. 



4. Humerus of a fossil sirenian from the same locality as Ij'ptophocd. Anterior 



view. Cat. No. 5360. 



(AH the figure-s natural size.) 

 - J — , 



('G. B. Shattuck, Geological and paleontological relations, with a review of earlier 

 investigations, Rept. Maryland Geol. Surv., Miocene, Text, 1904, pp. Ixxxvi to xcii. 



^Pt.T. Van Beneden — Description des Ossements Fossiles des environs d'Anvers, 

 Ire Partie, Pinnipedes, Ann. Mus. Roy. d' Hist. Nat. Belg., I, 1877, p. 79. 



