NO. 1699. 



Oy EDESTUS AND RELATED GENERA— HAY. 



47 



sheaths, even of old individuals, might have separated from one an- 

 other. The t3'pe of E. I'arpinslii lateh^ described by Missuna « is 

 evidently a segment produced by an adult indi- 

 vidual and freed from all its predecessors. 



At a short distance behind its anterior end 

 each sheath of E. crenidatus is divided on the 

 midline below into right and left portions, the 

 lower edges of which run forward and upward. 

 This is the origin of the groove which occupies 

 the lower border of the front of the shaft. It 

 is j^robable that in this groove at the point of 

 sej)aration of the lateral portions of the sheath 

 the nerves and blood vessels entered and ex- 

 tended backward into each sheath and tooth. 



It is, of course, possible that another tooth 

 would have been produced behind the sixth of 

 the type of E. crenidatus ; but, in as much as that 

 last tooth is considerabl}" thinner than its prede- 

 cessors, it is not unlikely that old age and de- 

 cadence of powers had come on and that no more 

 t^eth would have been developed. 



EDESTUS SERRATUS, new species. 



The history of the type of this species is 



exactly that of the specimen described as E. 



crenulatus. It is Cat. No. G049 in the U. S. 



The length of the fossil (pi. 12, fig. 4), as found, is 150 mm. The 

 sixth and last tooth of the series had been broken 

 off before the time of entombment. If an allow- 

 ance of 27 mm. is made for this missing part the 

 whole length will be 177 mm. The greatest 

 height, from the apex of the second tooth down- 

 ward, is 51 mm. The greatest height of the shaft, 

 between the second and third teeth, is 35 mm. 

 Its greatest thickness is 21 mm. ; that at the rear 

 of the fifth tooth is 9 mm. The form of the shaft 

 and sections of it (text figs. 3, 4) resemble those 

 of E. crenidatus^ but the hinder section, though 

 not so high as that of E. crenulatus^ is fully as 

 broad. The last sheath occupies two-thirds of 

 the width of the shaft. The anterior half of the 

 shaft is rough, with close-set patches of enamel, 

 irregular in size and form. The hinder half 

 also is rough for some distance below the teeth, 



but most of the surface is nearly smooth. It seems possible that the 



hinder part of the shaft had been embraced by a sheath that had not 



Fig. 3. — Edestus serr>- 



TUS, Xl. TYPE. SEC- 

 TION BETWEEN FIRST 

 AND SECOND TEETH. 

 1, HINDER END OF 

 FIRST TOOTH ; 2, 



ENAMELED PROCESS OF 

 SECOND TOOTH ; 3, 

 SHEATH OF THIRD 

 TOOTH ; 4, SHEATH OF 

 FOURTH TOOTH ; 5, 

 SHEATH OF FIFTH 

 TOOTH ; 6, UPPER BOR- 

 DER OF SHEATH OF 

 SIXTH TOOTH ; 7, 



GROOVE ALONG LOWER 

 BORDER OF ANTERIOR 

 HALF OF SHAFT. 



National Museum. 



Fig. 4. — Edestus serra- 

 tds, x 1. type. sec- 

 tion between third 

 and fourth teeth. 

 3, hinder end of 

 third tooth ; 4, 

 enameled process of 

 fourth tooth ; 5, 

 sheath of fifth 

 tooth ; 6, upper bor- 

 der of sheath of 

 sixth tooth. 



* Bull. Soc. Imp. Nat. Moscow, vol. 21, 1908. p. 528. 



