NO. 9 NEW CAMBRIAN TRILOBITE FAUNULE — RASETTI 17 



Type species. — Bathydiscus dolichometopus Rasetti, new species. 



Occurrence. — Late Lower Cambrian of New York. 



Discxission. — The cephalon indicates close relationship to Oodis- 

 cus as evidenced by the same general shape, characters of glabella 

 and occipital ring, position of the geniculation and spine on the 

 posterior border. The chief difference is the extension of the glabella 

 encroaching upon the anterior border furrow and the peculiar inbend 

 of the latter at the sides. Another important feature is the arched 

 anterior border, which does not occur in Oodiscus. If the pygidium 

 is correctly assigned, its peculiar doublure represents one of the most 

 characteristic features of the genus. 



BATHYDISCUS DOLICHOMETOPUS Raaetti, new species 

 Plate 1, figure 3 ; plate 9, figures 1-16 



Available material. — Several cephala and about an equal nimiber 

 of pygidia. 



Description. — Cephalon highly convex, semielliptical, well 

 rounded in front. Glabella strongly elevated, slightly pear-shaped, 

 well rounded in front, totally unfurrowed. Occipital furrow very 

 shallow at the sides, obsolete medially ; occipital ring very short, con- 

 tinuing the longitudinal profile of the glabella, extended farther back- 

 ward than the cheeks. Cheeks very convex, laterally sloping down 

 vertically to the border furrow. Border furrow well impressed, later- 

 ally paralleling the cephalic margin, anteriorly inbent at each side 

 to merge with the axial furrow that separates the front of the glabella 

 from the border. Border convex, wide, lacking tubercles. Cephalic 

 doublure very narrow, normally reflexed. Border in anterior view 

 arched medially, paralleled by the border furrow which rises on each 

 side to meet the axial furrow. The pygidium is referred to the species 

 chiefly on account of the position of the geniculation and the fit of 

 the up-arched anterior border of the cephalon and down-arched 

 posterior border of the pygidium, an arrangement that must have 

 ensured a close fit of the two shields in enrollment. Pygidium widest 

 at anterior end, semielliptical, with strong relief. Axis elevated, well 

 defined by the axial furrow, tapered, occupying about three- fourths 

 of the pygidial length, unfurrowed. Articulating half-ring short (sag.), 

 defined by a deep articulating furrow. Pleural regions convex and 

 downsloping. Anterior border with sharp geniculation at one-third the 

 distance from the axial furrow to the lateral margin ; articulating facet 

 well developed. Border narrow and but slightly elevated laterally, 

 defined by a very shallow border furrow, but elevated at the level 



