74 SAiSr DIEGO SOCIETY OP NATURAE HISTORY 



RAYMOND (Percy E)— Continued 



Niobe, Sympliysurus and Basilicus, are more primitive than Isotelus, Nileus, Ptvchopvge, 

 Hemigyraspis and Asaphellus. 



The author quotes Brogger'H studies on tlie hypostoma and his division of tliree dis- 

 tinct types. 



Pointed beliind, Megalaspis and Ogygiocaris. 



Quadrate, N'lohe insignis. 



Extended behind into two long, large prongs, Asaplius, Isotelus, etc. He remarks 

 under the Geologic range, that the Asaphids appear earlier in America and ha\e a 

 longer range than in any dther country. 



The Cambrian, which liave entire hypostomas, consists of the genera Ogygopsis, 

 Illaenurus, Sympihysurus, Asaphellus, Hemigyraspis and Megalaspis. 



Ordovican, Beekmantown, the Asaphids are less varied as only Isoteloides and 

 Nileus are present. 



In the Chazy, Isotelus, Isoteloides, Basilicus, Onchometopsus, Vogdesia and Nileus 

 occur. 



In tlie Silurian, in the Lowviiie (Silurian) and Back River (Ordovian), the genera 

 Oncliometopus, Isotelus, Isoteloides, Basilicas and Vogdesia. 



In the Trenton there are, so far as is now known, only Isotelus and Isoteloides. 



In the Citica, Isotelus and t)gygites. 



In the Richmond, Isotelus, Onchometopus, Brachyaspis and probably Ogygites. 



The autiior uses Asaplius cxpansiis as the type of the genus, which is characterized 

 by its short, broad head, and pygidium from which all depressed borders are absent; 

 by the rather prominent glabella, which expands towards the front and reaches the 

 anterior margin; the large eyes; the course of the anterior portion of the frontal suture, 

 which meets in a point in front of the eye; and the short pygidimn, with narrow, well- 

 defined axial lobe and smooth pleural lobes. 



The genus is well developed in the Baltic Region. 



Under the heading of lines of development from the Asaplius, the author remarks 

 that the variation in the Ordovician Baltic species seems to be in the direction of the 

 obliteration of furrows on the surface; that is a further loss of evidence of original 

 segmentation in cephalon and pygidium. 



Onchometopus differs from Asaphus, in liaving tlie glabella less marked, the axial 

 lobe of the thorax wider, the thoracic segments flatter, the axial lobe of the pygidium 

 less convex and without rings. 



Megalaspiides, like Asaphus, with narrow axial lobe, expanding glabella, no de- 

 pressed border on the pygidium, but with a narrow one on the front of the cephalon. 



Isoteloides, in which both the cephalon and pygidium have depressed borders. 



Isotelus, in which the axial lobe of the thorax is wide, the glabella and the axial 

 lobe of the pygidium so ill-defined as to merge into the general surface of the head; 

 therefore, both these smooth trilobites and species of Brachyaspis and Onchometopus 

 are so like Isotelus, that the three genera can only be separated by their lines of de- 

 velopment. 



Basilicus is a primitive genus, with forked hypostoma, with a strongly ribbed tail; 

 the facial suture marginal in front, and the glabella strongly outlined and shows 

 glabella furrows. 



The author remarks from Basilicus, Ogygites seems to have developed. 



Tromelin and I.ebesconte, Assoc. Francaise, Adv. Sci., 1875, p. 33, use the new generic 

 name of Ogygites for Brongniart's Ogygia, it having been used for other genera in 

 natural history. These authors use O. Desmaresti Brog. for the type, and include O. 

 Brongniarti Rou. as a syn. The same authors refer Ogygia, the first species described 

 under the genus by Brongniart, to the genus Asaphus. 



