ART. 19 A MIOCENE POEPOISE PROM MARYLAND KELLOGG 39 



arches and at the posterosuperior angle, there is a well-defined facet 

 for the accommodation of the head of the following rib. Anteriorly 

 the diapophyses arise high up on the neural arch and gradually 

 shift their position to a lower level from the first to the seventh 

 dorsal, but on the eighth the shift is more noticeable since each 

 process arises from the side of the neural arch about midway be- 

 tween the centrum and the top of the neural canal. The postzygapo- 

 physial facets become progressively shorter toward the posterior end 

 of the dorsal series and disappear entirely on the first lumbar. 



Fh'st dorsal. — The anterior dorsal of this porpoise exhibits the 

 structural pecularities which characterize the first dorsals of most 

 living delphinoids. The centrum is nearly three times as wide as 

 long and the usual facet for the capitulum of the second rib is sit- 

 uated at the base of the neural arch on the posterosuperior lateral 

 border of the centrum. The neural spine is especially slender and 

 is curved from base to apex. The neural arch is low, stout, and nar- 

 row anteroposteriorly, with a lateral diapophysis on each side which 

 bears a large articular facet for the tuberculum of the first rib. 

 The articular facet which occupies the extremity of this process 

 slopes downward and inward. The neck of the diapophysis is con- 

 stricted dorsoventrally between the facet and the neural arch. The 

 postzygapophysial facets are large, elongate, and slope obliquely in- 

 ward. Both epiphyses are missing. 



Second dorsal. — Compared with the first dorsal, the centrum is 

 longer, the neural spine is higher, and the articular facet for the 

 tuberculum of the third rib is slightly smaller. The neural spine is 

 slender, but less strongly curved than that of the first dorsal. There 

 is a medium-sized facet for the capitulum of the third rib at the pos- 

 terior end of the centrum in the usual position. The neural arch is 

 of approximately the same proportions as on the preceding dorsaL 

 The posterior epiphysis is missing and the anterior one is separated 

 from the centrum, 



Thi7'd dorsal. — The centrum of this dorsal is almost twice as long 

 as that of the first. The neural spine tapers to the extremity and 

 is the least curved of the three anterior dorsals. The diapophyses 

 have shorter necks and the facets for the capitula of the fourth ribs 

 are considerably larger than on the preceding vertebra. The pos- 

 terior epiphysis is attached to the centrum, but the anterior epiphysis 

 is loose and projects laterally beyond it on the left side. 



Fourth dorsal. — The centrum is more than one-half as long as 

 broad. Both epiphyses are attached to the centrum. This vertebra 

 is further characterized by shorter diapophyses and the neural spine 

 is of approximately the same width throughout. Compared with 

 the same vertebra of Delphinodon dividum the centrum is proper- 



