l62 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



a strong occipital furrow ; frontal limb of medium width, and arch- 

 ing up into a broad convex frontal border. Fixed cheeks narrow 

 and separated from the glabella by a strong, narrow furrow from 

 which they slope upward to the small palpebral lobes, which are 

 situated opposite the anterior end of the glabella; postero-lateral 

 limbs large, rounded at the genal angles. Free cheek elongate, 

 broad at anterior end, where it joins the frontal limb and border. 

 Eye lobe small and prominent at the inner anterior angle of the 

 cheek. 



The facial suture cuts the outer postero-lateral side of the cephalon 

 in advance of the genal angle, and passes almost directly inward to 

 the base of the eye; arching over the eye, it passes with a slight 

 outward curve forward to the front margin. 



Thorax with 42 segments; axial lobe convex with each segment 

 strongly rounded ; pleural lobes convex with each segment carrying 

 a strong flat furrow from the inner end nearly to the outer termina- 

 tion of the segment. 



Pygidium very small ; axial lobe well defined and broken into two 

 or three rings and a terminal section by transverse furrows ; pleural 

 lobes smooth in cast of test, but probably marked by faint, short, 

 backward-curving furrows. 



Surface unknown except that the casts in a fine sandstone are 

 smooth. 



Dimensions. — The largest cranidium indicates that some dorsal 

 shields had a length of at least 45 mm. 



Genotype. — Conocephalites calymenoides Whitfield. 



Stratigraphic range. — Upper Cambrian : Eau Claire formation. 



Geographic distribution. — Upper Mississippi Valley in central 

 western Wisconsin and eastern Minnesota. 



Observations. — This very remarkable trilobite resembles the genus 

 Calymene in the form of the cranidium and free cheeks, while the 

 thoracic segments have the straight, strong pleural furrow of Pty- 

 choparia. The great number (42) of segments is a very primitive 

 character and gives the thorax an annelidian aspect. 



MENOMONIA CALYMENOIDES (Whitfield) 



Plate 26, figs. 4, ^a-d 



Conocephalites calymenoides Whitfield, 1878, Ann. Rept. Geol. Survey 

 Wisconsin for 1877, p. 52. (Original description.) 



Conocephalites calymenoides Whitfield, 1882, Geol. Wisconsin, Vol. 4, 

 p. 179, pi. 3, figs. 2-5. (Describes and illustrates species.) 



Conocephalites calymenoides Whitfield, Chamberlin, 1883, Geol. Wiscon- 

 sin, Vol. I, p. 131, fig. i7d. (Reproduces fig. 2 of Whitfield in Vol. 4.) 



