A NEW FOSSIL PORPOISE FROM MARYLAND. 



189 



Palatines in contact in the median line throughout their length; their surface 



concave posteriorly. Descending wings of the basi-sphenoid 



transverse ridge. 

 Teeth about 



ith a strong 



27 — 27 



26 — 26 y 



sm 



ill, with an average diameter at the base of the 

 crown of 5.2 mm., and total length about 29 mm. ; more or less flattened anteriorly 

 and posteriorly. Crowns short and strongly recurved, especially near the pos- 

 terior end of the series. Last superior tooth with two accessory cusps behind 

 the main cusp. Other posterior teeth with an accessory cusp on each side of the 

 main one, and a bifurcated antero-external longitudinal ridge, and simple postrro- 

 internal ridge. 



Type-specimen: Cat. No. 7278 U. S. Nat. Mus. Skeleton from the Calvert 

 Cliffs, Chesapeake Bay, Maryland, one mile south of Chesapeake Beach. 



Col- 

 lected May 30, 1908, by William Palmer. Preserved in the U. S. National 

 Museum. 



Relationships. 



The remarkable fossil remains described above throw a strong light on the 

 origin of the existing typical dolphins. There can be no doubt that the genus 

 belongs to the family Delphinidae, but it is distinguished from all others of that 

 family in that the posterior teeth are distinctly tuberculate. 



The Delphinidse, as is well known, are characterized by the numerous teeth 

 in both jaws, very broad occipital region, conjoined lachrymal and malar hones, 

 inflated pterygoid bones, broad and rather flat frontal plates of the maxilla*, 

 slightly concave prenarial region (typically), anchylosed atlas and axis (the former 

 with a single transverse process), anterior ribs with both tubercle and neck, 

 ossified sternal ribs. 



The form under consideration presents most of these characters, the devia- 

 tions therefrom being chiefly such as one would expect to find in a primitive form. 

 Thus, the atlas and axis are separate, but when placed in contact it is seen that 

 they present the same general form as the conjoined bones of recent species. 

 The pterygoid bones are lacking in the specimen described, as is usually the case 

 with fossil skulls of cetaceans, but the impressions remaining indicate that they 

 had the same general form as those of recent delphinoids. The sternal ribs are 

 also lacking, having no doubt remained cartilaginous owing to the immaturity 

 of the individual. 



The most striking primitive characters of the species are the rugosity of the 

 enamel layer of the teeth and the presence of anterior and posterior ridges and 

 accessory cusps. The teeth of recent typical delphinoids, with the exception of 

 Steno, have smooth crowns. In Steno the rugosity is distinguishable with the 

 naked eye, and under a glass it is seen also that the majority of the teeth have 

 anterior and posterior ridges, which extend downward from the apex at least 

 to the middle of the crown. This peculiarity in a genus which otherwise presents 

 the characters of a typical delphinoid, is extremely interesting, and points to 

 affinity with the fossil genus. Accessory cusps, or tubercles, are not observable 



