CETOTHERES FROM THE MIOCENE CHOPTANK FORMATION 



39 



Fifth chevron. — The anterior projection of the 

 haemal spine on this chevron (pi. 20, fig. 10) is short and 

 acuminate ; the posterior projection is considerably elon- 

 gated and there is a median indentation on the ventral 

 edge. The wide (31 mm.) articular facets (length, 60 

 mm.) are attenuated anteriorly and rounded posteriorly. 



Sixth chevron. — A median indentation on the ven- 

 tral edge of the haemal spine as well as a short anterior 

 projection and a rather dee^j posterior projection are the 

 most obvious profile alterations (pi. 20, fig. 11). The 

 articular facets (length, 63 mm.) are attenuated at both 

 ends and somewhat narrower (28 mm.) than on the pre- 

 ceding chevron. Deep scratches by shark teeth, especially 

 on the left side, are present on the haemal spine. 



Seventh chevron. — Elongated (58 mm.) but nar- 

 rower (24 mm.) articular facets, strongly attenuated at 

 both ends, shorter anterior and posterior projections of 



the haemal spine and a much narrower haemal canal 

 characterize this chevron (pi. 20, fig. 12). 



Eighth chevron.— This chevron (pi. 20, fig. 13) is 

 about half the size of the preceding, the haemal spine 

 being markedly reduced; the posterior projection is 

 short and distinct. The elongated (52 mm.), anteriorly 

 and posteriorly attenuated, and transversely narrowed 

 (20 mm.) articular facets enclose an even smaller haemal 

 canal than that of the preceding chevron. 



Ninth chevron.— This is the smallest (pi. 20, fig. 14) 

 chevron of the six associated with this skeleton. The 

 thick haemal spine lacks a projection at either end. Each 

 articular facet is elongated (34 mm.), more noticeably 

 .attenuated at the anterior end than posteriorly, and 

 separated from the opposite facet by a minimum interval 

 of 7 mm. 



