PALEONTOLOGIC CONTRIBUTIONS I23 



These measurements indicate a trilobite even larger than Cer- 

 arus dentatus, the largest American Ceraurus previously 

 known. An incomplete specimen of that species has an estimated 

 length of about ioo mm, while C. ruedemanni should have 

 been about 125 mm long, if it had the same proportion of length 

 of cephalon to length of body that has been observed in C . den- 

 tatus. This measurement would not include the long pygidial 

 spines, but would be the length along the axial line. 



This species has about the same size as Ceraurus scutiger 

 Eichwald, the European (Russian) species which it most resembles. 

 The largest specimen of that species has, according to the measure- 

 ments given by Schmidt, the cephalon 35 mm long; the glabella 

 26 mm long, and 23 mm wide at the front and 21 mm behind. 



Comparison with other species. The presence of two pairs of 

 long spines in the pygidium of this species distinguishes it at once 

 from all other American species of Ceraurus. Among European 

 species, there is one which in size and spinose pygidium, very 

 strongly suggests our Chazy form. This is the Ceraurus 

 scutiger of Eichwald, from the " Brandschiefer " of the 

 Kuckers formation in Esthonia, Russia. This species was 

 described by Eichwald in 1857 on page 209 of the Bulletin de la 

 Societe des Natur. de Moscou, and in the same year figured with 

 out a name by Nieszkowski in the Archiv. f. Natur. Livland, 

 Estland u. Kurland, series 1, volume 1, plate 1, figure 13, plate 3, 

 figure 16. In 1859, Nieszkowski applied the name Cheirurus 

 spinulosus to the species and Schmidt has, without right, 

 adopted this name in his " Monograph of the East Baltic Silurian 

 Trilobites " (Mem. Imp. Acad. Sci. St Petersbourg, ser. 7, v. 30, 

 no. 1, p. 147, pi. 6, fig. 16; pi. 7, fig. 6-17; pi. 16, figs. 5, 6. 1881.) 



This species is of about the same size as Ceraurus ruede- 

 manni, is a true Ceraurus, and is in many ways like our Chazy 

 species. The glabella differs in the ornamentation, having rather 

 large tubercles on the posterior portion and being smooth at the 

 anterior end, while the whole of the glabella of C. ruede- 

 manni is covered with small tubercles. The glabella of C . 

 scutiger does not show the longitudinal furrows isolating the 

 axial lobe. On the pygidium one sees both the greatest similarities 

 and the greatest differences. In C. scutiger the pygidium 

 shows three pairs of spines and a short median spine, the pleura 

 of the third as well as the second segment being produced into 

 spines. 



