94 Forty-fourth Report ojv the State Museum, 



are usually of small size a.nd are widely distributed, having a very 

 considerable vertical range from the lower Silurian into the middle 

 or upper Devonian. They are subject to variation in some features, 

 especially in the number and arrangement of the spines upon the 

 pygidium, and in this respect afford no means of distinction from the 

 members of other divisions of the genus Ceratocephala. 



In 1839 Emmrich proposed"*" the term Odontopleura, apparently 

 not in ignorance of Murchison's term, but because he considered 

 it insufficiently defined in being based upon a fragmentary specimen. 

 He described and figured Odontopleura ovata, Emmrich, which must 

 be taken as typical of his proposed genus. This species was after- 

 wards refigured by him in 1845f under the name 0. bispinosa. A 

 highly finished figure of this species, was also given by Burmeister in 

 1843, J made, as it is stated, from the original specimen under the direc- 

 tion of the late H. Von Dechen,§^and from these figures it appears 

 that the species is characterized by the great breadth of body, and by 

 the occipital ring being smooth, or with a central tubercle, but 

 without spines. 



In 1840 Conrad described the species Acidaspis tuber culatus,\\ a well- 

 known form of the Lower Helderberg fauna, his description being 

 based upon the intra- sutural portion of a cephalon. The species is 

 strictly congeneric with A. Brighti, Murchison. At the same time he 

 described without figure or specific designation a fossil to which he 

 gave the name Acantholoma,*! and it would appear both from his 

 description and from the opinion expressed by Professor Hall in 1859 ** 

 that the author had under consideration a free cheek of the same 

 species of Acidaspis. 



In the report for 1841, Conrad proposed f f the name Dicranurus for 

 a fossil there figured, also from the Lower Helderberg fauna. This 

 form was mentioned in a list given on a preceding page of the same 

 report as Dicranurus hamatus and under the name Acidaspis hamata it 

 has become known as one of the peculiar species of this fauna. The 



* De Trilobitis, p. 35, plate, fig. 3. 



f'Ueber die Trilobiten," (Neues Jahrbuch fiir Mineralogie, etc). 



t Organization der Trilobiten, pi. 2, fig. 11. • 



§ Burmeister states that this specimen in the Museum of the University of Berlin, was 

 the only one known of the species, and Heidenhain in 1869 makes the same statement 

 (Zeitschrift der deutsehen geologischen Gesellschaft, vol. 21. p. 167). 



II Third Annual Report on the Palseontological Department of the Survey, p. 205, fig. 3 

 of the plate accompanying a few copies of the report for the following year. (See 

 Fifteenth Report N. Y. State Cabinet.) 



H In his report for the following year Conrad used the term Acantholoma spinosa in a 

 list of fossils, but without further definition. 



** Palaeontology of New York, vol. 3. p. 370, 



tt Page 48, plate, fig. l. 



