HORN EXPEDITION — PALyEONTOLOGY. 101 



Opthoceras, sp. Etheridge, fils. 



Ref. — vi., pi. iii., figs. 13-15. 



I have nothing to adtl to Mr. Ethciidge'.s description except to oljserve that 

 the resemljhmce to Actinoceras tatei is \ery considerable, though tiie siphuncle is 

 rehitively much .smaller and the sutures direct. 



Endoceras warburtoni, Eth., tils. 



Ref. — iv., p. 7., pi. i., tigs. 12, 1-3, and vi., p. 20, pi. iii., ligs. l(J-20. 



i\Ir. Etheridge in IS'Jl (4) Hgured three siphonal casts presumably of this 

 species. I now further supplement this interesting discovery by the pourtrayal of 

 a specimen /;/ situ (PI. IT., Figs. \\a, 11/'), though from the greater rate of increase 

 ill size of the siphon (one in ten as against one in twenty-three or twenty -four) 

 probably indicates a distinct species. The stoutest specimen has a diameter of 

 35 mm., and indicates a rate of increase of about one in eleven. 



Loc. — In limestone, near camp on Laurie's Creek, nortli of Tempo Vale, 

 Petermann Creek. 



Endoceras arenarium, sp. nov. (Plate I., Fig. I.) 



Sp. char. — iShcll straight, section elliptical (the I'atio of the two diameters 

 about six to seven), rate of increase about one in seven or eight. Siphuncular 

 ca\ity included within the septa, marginal, elliptic (the ratio of the two diameters 

 about eleven to twelve), occupying nearly one-lialf of the hunger dianu;ter of the 

 shell. Septal chambers \'arying from 3 to 7 mm. wide at the circumferential 

 margin, where the longer diameter of the shell is 84 nun. Septa very convex, 

 broadly imbricating exteriorly, and deeply and abruj)tly descending at the alveolar 

 cavity. Test and body-chamber unknown, though the cast of the septal })ortion of 

 the shell is smooth. ' 



This species attained to a large size ; a portion has the following dimensions : 

 Length, 85 mm. ; diameters of the broader end, 81 mm. and 73 nun. ; diameters 

 of the narrower end, 75 nun. and 09 mm. ; diameters of the siphuncle at the 

 broader end, 335 mm. and 18'5 mm. Tlu; rate of increase of this and other 

 examples indicates a distal extension of two feet three inches, but a specimen 

 collected at Finke Pass (though not preserved) was quite twice as bulky as the 

 example just (pioted. The specimens seem to indicate a distinct species by the 

 elliptic section of the siphuncular cavity. 



