NOTES ON THE ZEUGLODON— LUCAS. 329 



that they have to be chiseled out. While the associated invertebrate fossils are 

 numerous, but few others than those mentioned can be gathered, due to the incoher- 

 ent, chalky nature of the test or its complete removal by water. 



The following generalized section shows the horizon in Choctaw County, .Via., for 

 B(i.s-il()!<(iiinis. 



Oriieralizf'd sficdon of Ihf Zeuglodon lied [Icnniiiohu/!/ Ihul of IT. //. Dull.) 



Oligocene Vickslnirgian (Red Bluff formation): 



Iron-stained, reddish marl, with a liardened ban<I about :> feet tliick nt-ar thecen- 



ter. The characteristic fossils are O^ireo rlckshnnji-iiKis, S/ioikIi/Iks (lumosuH, 



and Pe'cten cocomius. About 10 feet seen. 

 Eocene Jacksonian (Zeuglodon beds): 



Soft yellowish-white marl abounding in small lime concretions and foraminifera. 



But one occurrence of Bcmlosauru^ known here. Thickness, about 5 feet. 

 Echinoid bed. Invertebrates of a few sjiecies common — Hemiaster, Terehratu- 



lina, and Ostreafalco. The general horizon for Basilosaurus, Dorudon, and 



other vertebrates inunediately below the echinoids and throughout the next 



zone. Thickness, 2 feet. 

 Soft whitish marl abounding in Pecten perplanus, Ostrea trigonalii, and Bryozoa; 



also Cj/prrea fenestralis, Auria alnbamensis, and Scala raneUina. Thickness, 7 



feet. 

 Other Jacksonian horizons come here, followed by the Claiboruian. 



In spite of the number of vertebraj present, these two series do not 

 seem to qfliite complete the vertebral colmnn, which apparentl}' lacks 

 one or two at the point of junction of the two series. The niunber so 

 far known is 58, distributed as follows: Cervicals T, dorsals 13, lumbo- 

 caudals 38. 



Associated with the second series of bones were the two o.^sa innomi- 

 nata, one of which was found near the twenty-tirst vertebra counting 

 from the posterior end of the series, the other near the twenty -second, 

 as well as a bone considered to be the femur. 



As this skeleton had been but little washed about after deposition, 

 th<^ chances or probabilities are that the pelvis lielongs somewhere 

 near these verte))riv. 



Neither of the l)ones appears quite complete, but there is some rea- 

 son to suppose that the abruptly truncated posterior end of the left 

 OS iiuiominatmu is natural, and not, as the first o-lance sugoests, the 

 rosidt of a fracture. This supposition is based on the fact that the 

 straight posterior end is slightly roughened, as if it liad been, as in so 

 many animals, capped or terminated by a cartilaginous epiphysis. 



The pelvis of the eared seals, Ot((ril(l(i\ seems to throw the most light 

 on the morphology of the pelvis (just as the skull of Eametopias was 

 of the most service in restoring th(^ cranium), and by its aid wc are 

 able to say that ilium, ischiinn, and pid)is are all present, although the 

 ilium is almost aborted and the component ])ones are fused in one. 



The pectineal process, which is large, arises from the ilium, and not 

 the pubis, as is shown by the pelvis of a 3'oimg fur seal. 



The obturator foramen is large, and seems, in spite of the degenerate 



