RAYMOND AND BARTON: AMERICAN SPECIES OF CERAURUS. 533 



Numbers 4 and 5 are adults of typical size, and number 6 is the 

 largest complete specimen from Trenton Falls. Number 7 is one of the 

 plaster of paris casts of Green's type. 



In Vodges's Catalogue of trilobites, nineteen species of "Ceraurus" 

 are listed, but the name is there used in a very wide sense, and includes 

 species of Pseudosphaerexochus, Nieszkowskia, Heliomera, Ceraurus, 

 and Cheirurus. The only species with which Ceraurus pleurexanthe- 

 mus need be compared are C. dentatus, C. millcranus, C. hudsoni, C. 

 misneri, and C. pompiUus, and the differences from each are listed 

 under the appropriate headings on later pages. 



Note on Ceraurus pleurexanthemus. — Since the above was written, 

 fascicle 1 of series 4 of the Palaeontologia universalis (dated July, 

 1912) has come to hand. Leaves 236 and 236a, written by Dr. 

 Rudolph Ruedemann, are devoted to the figures and description of 

 Ceraurus pleurexanthemus. The type, which is in the New York 

 State Museum, is represented by a photographic figure which shows 

 more detail than can be seen on Green's casts, and leaves no doubt 

 that the original specimen is conspecific with the individuals so 

 common at Trenton Falls. As plesiotypes, three individuals are illus- 

 trated. The first, lettered P, is a fairly well preserved specimen of 

 Ceraurus pleurexanthemus from Trenton Falls, but as it has lost both 

 eyes and the pygidium is buried, it does not show the important char- 

 acters of the species. Through a typographical error, this figure 

 is labeled as enlarged § times, but from its size, it would seem that 

 the meaning should be " X l^-" The other two figures, Pi and P2, are 

 photographs of casts of two specimens figured by Hall (Pal. N. Y., 

 1847, 1, pi. 65, fig. lm and pi. 66, fig. la). The originals of these 

 figures are in the American Museum of Natural History in New York. 

 Both are individuals of our Ceraurus dentatus. 



Ruedemann has accepted Schmidt's diagnosis of Cheirurus and is 

 therefore led to state that Ceraurus pleurexanthemus has the character- 

 istics of Cheirurus s. s. This we have shown in the introduction to 

 this paper is not in accordance with the facts. Schmidt was led by 

 his geographical position to accept the northern Ceraurus exsul as 

 the type of Cheirurus in place of the proper type, the southern Cheiru- 

 rus insignis. 



Formation and Locality. — This species occurs in the Black River 

 and Trenton at almost all localities where these formations are exposed. 

 It is less common in the Lowville, and is not positively known from any 

 formation older than the Lowville, or younger than the Trenton. 



