Maryland Geological Survey 507 



Dalmanites micrurus (Green) 

 Plate XCI, Figs. 10, 11 



Asaphus micrurus Green, 1832, Mon. Trilobites of North America, p. 56, cast 



19, fig. 3. 

 Dalmania micrurus Hall, 1859, Nat. Hist. N. Y., Pal., vol. iil, p. 359, pi. Ixxiv, 



figs. 13-20, 1861. 



Description. — Hall describes this species as follows : '•' Pygidium tri- 

 angular, convex, somewhat abruptly sloping at the sides, acute, attenuate 

 behind. Axis very prominent, faintly subangular in the middle above, 

 and regularly rounded towards the posterior extremity, rigid, scarcely 

 declining below, and abruptly elevated from the posterior marginal 

 border; a narrow angular ridge extending from the extremity of the axis 

 into the acute spinifonn caudal tennination. The number of articulations 

 in the axis is twenty or twenty-one, which are strongly defined, and some 

 of the anterior ones slightly bent forward, and sometimes a little more 

 prominent or almost nodose in the middle. Each of the lateral lobes is 

 marked by fourteen or fifteen (and, in one example, sixteen) ribs; the 

 anterior ones very regularly arching, while about four or five of the pos- 

 terior ones are turned backwards, approaching the parallel of the axis. 

 Each rib is marked by a narrow groove along its summit, continued to 

 where the ribs coalesce in the narrow marginal rim. The direction of 

 this suture, near the origin of the ribs, is a little below the middle, but, 

 in its course, approaches more nearly the upper margin. Surface granu- 

 lose, with a row of stronger granules or small pustules on each side of the 

 furrow marking the ribs, and still stronger ones on the middle of the an- 

 ntilations of the axis." Hall, 1859. 



The glabella is more truncate than in D. pleuroptyx. The chief and 

 most obvious distinction as figured and described by Hall is in the sharp- 

 ness of definition of the axial annulations of the pygidium, but even this is 

 variable. This axis is also more prominent than in D. pleuroptyx, espe- 

 cially the posterior extremity. 



Occurrence. — Helderberg Formatiox, !N"ew Scotland (?) MEiiBER. 

 Cumberland. Oriskany FoRitATiON, Eidgely Member. Cumberland. 



Collection. — IT. S. National Museum. 



[Ohern.] 



