THE OTTAWA NATURALIST 



VOL. XXIX. FEBRUARY, 1916. No. 1 1 



THE GENERA OF THE ODONTOPLEURIDAE. 



By Percy E. Raymond. 



Odontopleura {Acidaspis auct.) is essentially a Bohemian 

 genus, as may be seen if one contrasts the 40 species listed by 

 Barrande with the 2 species of Esthonia, the 12 or 15 species 

 of Scandinavia, and the same number in Great Britain. 



Practically the only attempt at a subdivision of the Odonto- 

 pleuridae is that of Dr. John M. Clarke.* He recognized six 

 subgenera of the genus Ceratocephala, viz., Ceratocephala s. s., 

 Acidaspis, Odontopleura, Dicranurus, Selenopeltis and Ancy- 

 ropyge. I adopted this classification in the second edition of 

 the Eastman-Zittel text book (1913), raising the subgenera to 

 generic rank, and grouping them under Burmeister's family 

 name Odontopleuridae. Recently I have had occasion to study 

 the very large collection of trilobites of this family in the Museum 

 of Comparative Zoology, and while I have been able to con- 

 tinue the use of the names listed above, I find that the defini- 

 tions and limits of the genera Odontopleura, Ceratocephala and 

 Acidaspis must be very considerably modified. 



Dr. Clarke's definitions of the three genera were as follows: 

 Odontopleura, occipital ring smooth or with a central tubercle; 

 Acidaspis, occipital ring with a single straight median spine; 

 Ceratocephala, occipital ring with two straight divergent spines. 

 This scheme was, of course, simplicity itself, and, so long as 

 applied to the American species alone, seemed to work very 

 well. If, however, one turns to plate 38 of Barrande's "Systeme 

 Silurien du Centre de la Boheme," and looks at the three figures 

 (22, 25 and 30) at the bottom of the plate, he sees at once that 

 this classification is not a natural one. The figures represent 

 Acidaspis dormitzeri Hawle and Corda, .4. dufrenoyi Barrande, 

 both from the Silurian, and .4. hoernesi Barrande, from the 

 Lower Devonian of Bohemia. In glabella, free cheeks, thorax 

 and pygidium, these species are exceedingly alike, yet the first 

 has a neck tubercle, so would be called Odontopleura, the second 



♦Notes on the Genus Acidaspis. 10th Rept. N.Y. State Geologist, 1891, p. 61. 



