196 ROYAL SOCIETY OF CANADA 



Bathyuriscus senectus, Billings sp. (PI. IV., tig. 4.) 



Bathyurus senectus, Bill., Geol. Vermont, vol. ii., p. 953, flgs. 359, ;360. 



Bathyurus senectus, Bill., Palaeozoic Fossils, vol. i., p. 15, flgs. 19, 20. 



Protypus senectus, Walcott, U. S. Geol. Surv., Bull. 30, p. 213, pi. xxxi., figs. 2, 

 2 b and 2 c. 



Protypus senectus, Wall., Fauna of Olenellus Zone, p. 655, pi. xcviii., figs. 7, 7 6 

 and c. 



On comparison of Billings's description with his figure, certain dis- 

 crepancies of measurement are obsei-vable. The figure does not show the 

 eye even of the length given by that author (three-quarters of a line), 

 and the cheek has the appearance of having been broken away. The 

 length of the glabella is given at 3J lines — it is actually 2h ; the difference 

 appears to be due to a practice of Billings of including the occipital ring 

 in the measurement of the glabella. It is evident that the type specimen 

 preserved in the Museum at Ottawa is not the example figured by 

 Billings, as it shows more than he describes, but it is of the same form and 

 dimensions; it shows the entire head-shield, except the apex of the occi- 

 pital ring. It, therefore, seems probable that Billings, getting a more 

 perfect specimen than the one he had described, used it as the type. 



This fossil has all the characters of an ancestral or larval form of 

 Ogygia {Bathyuriscus) producta, Hall and W., probably the former. I 

 find the eyelobe somewhat longer than Billings gives it, being about one 

 line (2 mm.) long ; the posterior angle of the head-shield (not described 

 by Billings) is somewhat extended, the posterior marginal fold being as 

 long as the width of the glabella in front : owing to the width of the 

 posterior mai-ginal furrow at its outer end, the eyelobe becomes almost 

 continuous. There are three furrows, as Billings has said, on the glabella, 

 but the distance of the anterior from the middle furrow led me to suspect 

 that there should be a fourth furrow ; this penultimate furrow (counting 

 from the back of the glabella) is obsolete, but its place is determinable by 

 a change in the ornamentation of the test ; the presence of this fourth 

 furrow, the general outline of the shield, and the surface ornamentation, 

 shows that this species is a derivative from the Paradoxides phylum. 

 Billings does not describe the course of the occipital and glabellar fur- 

 rows ; the outer third of the occipital furrow is turned backward, and 

 the middle third arched forward ; this allows of a wide occipital ring. 

 The first pair of glabellar furrows also turn backward, and are impressed 

 only in the outer third the second furrow, which impresses the side of the 

 glabella only, is more direct, but turns back at its faint inner end. The 

 third pair of furrows, as we have said, are obsolete, and their place is a 

 little behind the ocular fillet. The fourth pair is marked only by a pit 

 at the edge of the glabella, just opposite the end of the ocular fillet. This 

 fillet is broad and flat, and crossed by the surface ornamentation. 



