VOL. XII, 

 1889. 



PROCEEDINGS OF THE NATIONAL MUSEUM. 41 



nellus from Paradoxides. It was an error, as the finding of Olenellus 

 beneath Paradoxides abundantly proves. 



The discovery of more perfect specimens of 0. asaphoides shows that 

 that which I had identified as the facial suture is a raised line in the 

 cast of the interior of the shell that fills a depressed line occupying the 

 position of the suture. I have since found this raised line in many 

 specimens, but in none is there a true suture cutting through the shell, 

 as in Paradoxides and most other genera of trilobites. 



Subgenus Mesonacis Walcott. 



See Bull. U. S. Geol. Survey, No. 30, 1886, p. 158. 



With the discovery of entire specimens of Olenellus asaphoides. 0. 

 kjerulji, 0. miclewitzia, and O. broggeri. it appears that Mesonacis ver- 

 montana is to be grouped with them, and all referred to Mesonacis as a 

 subgenus, on account of the peculiar pygidium of Olenellus thompsoni, 

 the type of the genus, as compared with that of 0. (Mesonacis) ver- 

 montana, the type of the subgenus 0. (M.) vermontana. 



Olenellus (Mesonacis) asaphoides Emmons (sp.). 



See Bull. U. S. Geol. Survey, No. 30, 1886, p. 168. 



The discovery of entire specimens of this species shows that it has 

 eighteen segments in the thorax, and a small, transverse pygidium, of 

 the Paradoxides type. On each of the five, short posterior segments 

 of the thorax there is a long, slender spine that projects back over the 

 pygidium. The entire specimens were found at the original locality of 

 the species, near the old Reynolds Inn building, one mile west of North 

 Greenwich, Washington County, New York. 



Nat. Mas. Cat. Invt. Foss., No. 18350. 



Olenellus (M.) broggeri Walcott. 



Oleneltlus broggeri Walcott, 1888. Name proposed on exhibition of specimens at the 

 International Geological Congress, Loudon. Name used in " Nature,*' vol. 

 38, p. 551, 1888. 



General form ovate, the length and breadth nearly as 3 to 2 in com- 

 paring the length of the entire body with the width of the head. Head 

 broad, semicircular in outline aud moderately convex when preserved 

 in the limestone, but very much compressed in the shales. Margin 

 rather broad, but varying in width one-half in different individuals; it 

 is slightly rounded and separated from the frontal limb and cheeks by 

 a shallow groove and narrow, low ridge; posteriorly it terminates in a 

 comparatively short, strong spine. The posterior margin of the head, 

 between the glabella and postero-lateral spine, is broken just within the 

 latter by a deep notch and a short spine that corresponds to the " in- 

 terocular" spine (Ford) of Olenellus asaphoides and the spine at the 

 pleural angles of the posterior margin of the head of O. Ijendti ; a 

 low ridge extends from back of the eye, next to the glabella, out to the 



