540 bulletin: museum of comparative zoology. 



expanding glabella, and in lacking spines at the genal angles. Foerste 

 states that the glabella is 5.5 mm. wide at the back, and 9 mm. wide 

 at the front. As the glabella is 11 mm. long, the rate of expansion 

 is much greater than in Ceraurus milleranus, C. dentatus, or C. plcurc- 

 xanihemus. The eyes are about equally distant from both glabella 

 and the posterior margin of the cephalon, as in C. milleranus. The 

 species shows an approach to Cheirurus, in that the glabella occupies 

 a large portion of the cephalon. The pygidium was not described 

 by Foerste, and probably is not preserved on the type. 



Formation and Locality. — A rare species in the Whitewater bed 

 at the top of the Richmond, at Richmond, Indiana, and Dayton, Ohio. 



Ceraurus numitor (Billings). 

 Plate 1, fig. 5. 



Cheirurus numitor Billings, Catal. Silurian fossils of Anticosti. 

 Geol. surv. Canada, 1860, p. 27, fig. 11. 



This trilobite is rare and not at all well known, but is remarkable 

 for the possession of a long and stout spine which projects upward and 

 backward from the neck-ring. No other Ceraurus is known with such 

 a spine, and in the whole family of the Cheiruridae this feature is 

 paralleled only in the rare genus Youngia. Nieszkowskia, it is true, 

 has a central spine on the cephalon, but it springs from the glabella 

 and not from the neck-ring. Somewhat over-rating the importance 

 of this unusual spine, we were at first inclined to refer the species to 

 Youngia, but it seems to be a true Ceraurus. Billings described the 

 glabella as subcircular, which would make it in agreement with that 

 of Youngia. 1 Billings's type is lost, but a specimen in the M. C. Z. 

 collected in Anticosti by the Shaler Expedition, although poor, shows 

 that the glabella expands forward and is covered with pustules as in 

 Ceraurus. Moreover, the posterior glabellar furrows are deep, rather 

 wide, and are nearly perpendicular to the axis of the glabella, instead 

 of being faintly impressed and curving backward as in Youngia. This 

 specimen also shows that the eye is far forward, as in C. bispinosus. 

 The neck-spine, is, unfortunately, broken off. The pustulose character 



'See Lindstroem, Foerteckning pa Gotlands Siluriska Crustaceer. Kongl. vet.- 

 Akad., Foerhandlingar, 1885, no. 6, p. 49, pi. 18, fig. 11; also Reed, the Lower Paleo- 

 zoic trilobites of Girvan. Palaeontogr. soc, 1906, p. 148, pi. 19, fig. 8-12, Cheirurus 

 trispinosus Young, is the type. 



