CETOTHERES FROM THE MIOCENE CHOPTANK FORMATION 



33 



or less massive pedicle of the neural arch and maintains 

 its elevation above the dorsal face of the centrinn. On 

 the ninth dorsal, however, the bent upward transverse 

 process (parapophysis) projects outward solely from 

 the dorsoexternal surface of tlie centrum. At the extrem- 

 ity of each parapophysis is an elongated facet (length, 

 47 mm.; vertical diameter, 16 mm.), strongly concave 

 from end to end for the head of the ninth rib. The dis- 

 tance between the ends of the parapophyses is 194 mm. 

 and this distance progressively increases to the end of 

 the dorsal series. The narrow backward projecting post- 

 zygapophyses are markedly reduced in extent. The 

 neural spine (pi. 19, fig. 4) has incxeased in width (mini- 

 mum 78 mm.) and projects more upward than back- 

 ward; it rises 176 mm. above the roof of the neural 

 canal and its distal extremity is horizontally truncated. 

 The pedicles of the neural arch are quite thin (minimum 

 transverse width, 9 mm.) ; the minimum length of each 

 is 65 mm. A noticeable change in the contour (pi. 21, 

 fig. 1) and dimensions of the anterior face of the cen- 

 trum occurs on the ninth dorsal (vertical diameter, 81 

 mm.; transverse diameter, 103 mm.). No vestige of the 

 median ventral longitudinal ridge is present on this 

 centrum, the lateral and ventral surfaces being equally 

 depressed. 



Tenth dorsal. — This dorsal has a higher and wider 

 neural spine (minimm width, 84 mm.; pi. 19, fig. 5) and 

 it rises 186 mm. above the roof of the neural canal. 

 Longei", horizontally widened and dorsoventrally com- 

 pressed transverse processes (parapophyses), longer 

 centrum, and a narrower (36 mm.) neural canal also 

 distinguish this dorsal from the ninth dorsal. Each 

 parapophysis (pi. 21, fig. 2) projects outward and 

 obliquely upward from the upper portion of the lateral 

 surface of the centrum, but the bifurcated or deeply 

 indented distal end is probably abnormal. The posterior 

 end of this distal facet for the head of the tenth rib is 

 roughened, although the head of this rib may most prob- 

 ably have been attached for the most part in the anterior 

 indenture. The thin pedicles of the neural arch have 

 a slightly greater anteroposterior length than on the 

 ninth. The large metapophyses project obliquely up- 

 ward and extend forward beyond the level of the ante- 

 rior end of the centrum ; they rise 54 nun. above the 

 floor of the neural canal. Tlie prezygapophysial facets 

 are almost vestigial. The postzygapophysial facets, al- 

 though damaged, were obviously very narrow. The con- 

 tour and dimensions of the subcordate anterior face of 

 the centrum is similar to the nhitli. 



Eleventh dorsal. — Rather slender, dorsoventrally 

 compressed and backwardly curved parapophyses (pi. 

 21, fig. 3) whjch project outward from near the middle 



of the height of the lateral surface of the centrum char- 

 acterize this vertebra. The left transverse process is 

 missing. Tlie anterior edge of the i-ight parapophysis is 

 thin, the posterior edge thickened and rounded, and the 

 relatively small ovoidal (length, 34 mm.; vertical diam- 

 eter, 15 mm.) distal facet for the head of the eleventh 

 rib is located posteriorly on the distal end. The thin 

 pedicles of the neural arch slightly exceed in antero- 

 posterior diameter (69 mm.) those on the tenth dorsal. 

 The metapophyses are larger and less widely separated 

 than on the tenth dorsal. Neitlier prezygapophysial 

 nor postzygapophysial facets are discernible. The neural 

 spine (minimum width, 84 mm., pi. 19, fig. 6) is hori- 

 zontally truncated at the distal end, is slanted slightly 

 backward, and rises 208 mm. above the roof of the neural 

 canal. 



Twelfth dorsal. — The roughened rounded end of the 

 right parapophysis indicates that the head of the 

 twelfth rib was attached there. This right parapophysis 

 lacks portions of the anterior border, but sufficient 

 remains to suggest the original contour of this dorso- 

 ventrally compressed transverse process. The left 

 transverse process is not preserved. The large laterally 

 comj^ressed metapophyses rise 58 mm. above the floor of 

 the neural canal and were separated by a 38 mm. gap; 

 they project forward noticeably beyond the level of the 

 anterior end of the centium. Portions of the broad neural 

 spine (pi. 19, fig. 7) are missing and hence the original 

 height is uncertain. The extremity, however, was slightly 

 convex. The length of the centrum (108 mm.) exceeds 

 that ( 104 mm.) of the eleventh as does the vertical diam- 

 eter (90.5 mm.) of the anterior end. The transverse 

 diameter of the neural canal (pi. 21, fig. 4) diminishes 

 toward the first lumbar on most of the dorsal vertebrae. 



LUMBAR VERTEBRAE 



Assuming that the hnnbar series comprised twelve verte- 

 brae, an estimate based on progressive increase in the 

 length of the centra from the first to twelfth indicates 

 a total length of 1550 mm. (61 inches) . 



The bowed outward portion of the vertebral column 

 between the first and eleventh lumbars fell to the base 

 of the slope facing Cliesapeake Bay at some time during 

 the process of continued weathering and erosion. Tidal 

 action resulted in disintegration and dispersal of the 

 fallen bone fragments prior to discovery of the re- 

 mainder of the partially exposed skeleton. At the time 

 of excavation the first lumbar was found in contact with 

 the twelfth dorsal and the last two lumbars in a similar 

 relation with respect to the fii-st in the consecutive series 

 of caudals. 



