1898-1902. No. 32.] FOSSIL FAUNAS FROM SERIES B. 33 



Arthropoda. 



Crustacea. 



Trilobita. 



Proetidae. 



Proetus STEININGER. 



Proetiis leptorhachis nov. sp. 



PI. VIII, fig. 14. 



Only two pygidia are known of this species, both well preserved 

 and of exactly the same size. Their outline is semi-elliptical with greatest 

 length 9 mm., greatest width 1415 mm. The flat or faintly convex 

 marginal rim is separated from the strongly convex middle portion by a 

 well defined line of depression. 



The axis is prominent, slightly convex longitudinally and relatively 

 very narrow, the width being only about one-fourth of that of the 

 entire pygidium in the anterior region, the margins not very markedly 

 tapering towards the rounded, well defined end, which is situated a little 

 more than two mm. from the posterior border. The number of the 

 annulations 11 12. 



In the lateral parts of the pygidia on each side, we see 7 distinct 

 pleural lobes, with relatively broad interspaces, and indications of others 

 nearer the posterior end. Where the shell-substance is still preserved 

 the pleural lobes - which do not cross the marginal rim show the 

 longitudinal furrow very distinctly. 



The entire surface is covered by very small pustules, in a good 

 light visible to the naked eye. No regular arrangement can be noticed 

 in these pustules. 



As is indicated by the name proposed for this species one of the 

 chief characteristics is the relatively narrow axis. A form also known 

 only through a pygidium - - that is somewhat alike, is Proetus hesione 

 HALL (see Pal. New York, vol. 7, p. 93, pi. 20, figs. 1516) from the 

 Schoharie grit of New York. The axis of this species, though narrow, 

 is still relatively broader than in the new form in question, and further- 

 more the surface ornamentation is different. Another related form is 

 Proteus planimarginatus MEEK from the upper Helderberg of Ohio 

 (see Geol. Survey of Ohio, Paleontology, vol.1, p. 233, pi. 23, figs. 3 a b). 



3 



