THE OTTAWA NATURALIST 



VOL. XXX. OTTAWA, AUG. -SEPT.. 1916. Nos. 5 and 6 



PAEDEUMIAS AND THE MESON ACIDiE, WITH DESCRIP- 

 TION OF A NEW SPECIES, HAVING AT LEAST 

 44 SEGMENTS, FROM THE LOWER CAM- 

 BRIAN OF BRITISH COLUMBIA, (a) 



By Lancaster D. Burling. 



By common consent we are accustomed to regard the 

 Crustacea as derived from the annelids, and we have pointed 

 to their abundantly segmented body as a reason for assigning 

 this ancestorship to them. As late as 1915 (b) it was possible, 

 however, to say that there are never less than two nor more 

 than 29 segments in the thorax of a trilobite. Walcott (c) has 

 recently described and figured a specimen with 42 normal seg- 

 ments. The specimen to be described contains at least 44 

 segments (the end is broken away), 29 of which are rudimentary 

 segments posterior to a spine-bearing fifteenth. The great 

 number of segments gives sufficient interest to this trilobite 

 to warrant its description, and a discussion of its bearing on 

 the evolution of the Mesonacidae. 



Paedeumias robsonensis n. sp. 



Pazdeumias n. sp., Burling, 1916, Bull. Geol. Soc. America, vol. 27, 



pp. 158-159. 

 Pcedcumias n. sp., Burling, 1916, Geol. Surv. Canada, Sunim. Rept. 



for 1915, p. 100. 



Description. Outline of the cephalon almost semi-circular, 

 marginal rim relatively wide and flat, genal and intergenal 

 spines distinct. Glabella crushed in front, but apparently 

 parallel-sided and reaching in front to the marginal rim. Eyes 

 prominent, broad at the anterior end, where they merge into 

 and even cross portions of the glabella, and narrow at the pos- 

 terior end which lies just within the posterior margins, is raised, 

 and does not reach the sides of the glabella. Glabellar furrows 

 deeply marked, four pairs being visible in the unmashed portion 

 of the glabella described. The two posterior pairs are almost 

 transverse, and extend two-thirds of the way from the dorsal 

 furrow to the centre of the glabella; the third pair, counting 



() Published bv the permission of the Deputy Minister of Mines. 



(6) Schuchert, Pirsson and Schuchert's Textbook of Geologv, 1915, p. 606. 



(c) Smithsonian Misc. Coll., vol. 64, 1916, p. 162, pi. 26, figs". 4b, 4c. 



