1916] The Ottawa Naturalist. 137 



merits without a pronounced ridge; there are also a few which 

 agree with the type of Acidaspis in having a triangular glabella 

 and a broad stout nucal spine; a few others which have the 

 characteristics of Dicranurns, Sele)iopeltis, or Ancyropyge, but 

 the great majority have an oval glabella and a prominent 

 median ridge on the pleural portion of each thoracic segment, 

 as in Odonto pleura. Hence, the name given to the family by 

 Burmeister is not only the oldest, but is particularly appro- 

 priate. 



It is quite possible that the species which I have grouped 

 under Odontopleura can and will be arranged in other subgenera 

 or genera. The type is a very broad form, and a row of tubercles 

 on each of the thoracic segments is a prominent feature of the 

 ornamentation. With it could be associated 0. prevosti Bar- 

 rande, and 0. hughsi (Salter). Another group, with a narrower 

 form, fewer tubercles on the thorax, and fewer and longer spines 

 on the pygidium, is exemplified by 0. dufrenoyi, 0. hoernesi, 0. 

 roemeri, and other Bohemian species. A third group, with 

 thick, subequal pygidial spines, would include 0. pectinifera Bar- 

 rande, and O. cornuta (Salter). Then there is the exceedingly 

 spinose O. mira Barrande, with very numerous and small 

 pygidial spines, barbed lateral thoracic spines, and very tall 

 eyes. J^or the present, however, it seems useless to break up 

 the genus into such small groups. 



To replace my definitions in the Zittel-Eastman text book, 

 I would suggest the outline of the family which follows;— 



Family Odontopleuridae Burmeister. 



Opisthoparia with large free cheeks and eyes (usually), 

 far back and close to the glabella. Lateral lobes of the glabella 

 reduced to two or one. Thorax of 8 to 11 segments. All 

 parts of the test usually very spinose, the spines usually of 

 the horizontal type. 



Odontopleura, Emmrich. Glabella oval in outline. The 

 pleural lobe of each segment of the thorax has a narrow, strongly 

 elevated median ridge. Ordovician to Devonian. Cosmopolitan. 



Acidaspis, Murchison. Glabella roughly triangular in 

 outline, tapering towards the front. The pleural lobe of each 

 segment is divided by a linear furrow into a low anterior and 

 an elevated posterior ridge. Ordovician and Silurian. Europe 

 and North America. 



Ceratocephala, Warder. Free and fixed cheeks anchylosed, 

 eyes far forward and far from the glabella. The pleural lobe 

 of each thoracic segment is divided by a shallow median fur- 



