RAYMOND: NEW AND OLD SILURIAN TRILOBITES. / 



back, narrow axial lobe, and nine segments in the thorax. The 

 profiles of both shields are rather flat but uniformly convex curves. 

 (See especially Holm, Bihang Kogl. Vet. akad. Handl., 1883, 7, pi. 4, 

 f. l-l2). Holm was not able to see any value in this genus, pointing 

 out that the only real characteristic brought forward by Burmeister 

 and by Angelin was the presence of genal spines, and the species with 

 genal spines are so highly variable among themselves as to suggest 

 that this character in itself does not denote any real relationship. It 

 seems, however, that a certain group of illaenids can properly be de- 

 noted by this term, and the genus will be referred to later. 



Thaleops Conrad, 1843. 



Proc. Acad. nat. sci. Phil, 1843, 1, p. 331. 



Type, Thaleops ovata Conrad. 



The presence in this species of very high eyes on long peduncles, 

 long narrow genal spines, deep dorsal furrows sharply delineating a 

 prominent glabella, a narrow axial lobe, ten thoracic segments, and a 

 small short pygidium, mark an unusually well-defined genus which 

 seems to be confined to North America, and probably to the Ordovi- 

 cian, though one Silurian species has been referred to the genus. 



Alceste Hawle and Corda, 1847. 

 Prodr. monog. Bohm. tril., 1847, p. 66, pi. 4, f. 31.. 



Type, Alceste latissima Hawle and Corda (which is the same as 

 lUaenus hisingeri Barrande, according to Barrande). 



This genus is not valid, for it was based upon an immature speci- 

 men showing only four segments, and was very incorrectly described 

 and figured. Without Barrande's explanation, no one would be able 

 to identify the Alceste laiissima with any Bohemian trilobite. 



Rhodope Angelin, 1854. 



Pal. Scandinavia, 1854, pt. 1, Trilobita, p. 38, pi. 22, f. 17. 



Type, Rhodope lineata Angelin. 



The name Rhodope was used for a gastropod by von Siebold in 

 1848 (Anatomic, p. 296), and Volborth replaced the name by Panderia. 



