312 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



Olenellus Cole (in part), 1892, Natural Science, Vol. i, pp. 340-346. (A 

 historical discussion of Olenellus and many of the other forms now 

 placed in the family Mesonacidae.) 



Olenellus (Hall), Peach and Horne, 1892, Quart. Journ. Geol. Soc. 

 London, Vol. 48, p. 236. (Defines restricted use of Olenellus.) 



Olenellus (Hall), Bernard (in part), 1894, Quart. Journ. Geol. Soc. Lon- 

 don, Vol. 50, pp. 412, 419, 430. (Refers to Olenellus in discussing the 

 systematic position of the trilobites, but most of the references are 

 based on the study of forms now referred to Elliptocephala asaphoides.) 



Olenellus (Hall), Peach, 1894, Quart. Journ. Geol. Soc. London, Vol. 50, 

 pp. 671-673. (Refers to certain characters in connection with a dis- 

 cussion of the Scottish species of the genus.) 



Olenellus (Hall), Beecher, 1897, American Journ. Sci., 4th ser.. Vol. 3, p. 

 191. (Refers to genus in discussing classification and includes it 

 under family Paradoxince.) 



Olenellus Moberg. 1899, Geol. Foren. i Stockholm Forhandl., Bd. 21, 

 Hafte 4, p. 317. (Characterized. The genus is discussed frequently on 

 pages 309-320 of the paper.) 



Olenellus Weller (in part), 1900, Ann. Rept. Geol. Survey New Jersey 

 for 1899, pp. 50-51. (A discussion of the genus in its broader sense.) 



Olenellus (Hall), Pompeckj, 1901, Zeitschr. Deutschen geol. Gesellsch., 

 Vol. 53, Heft 2, pp. 14-17. (Olcnopsis is compared with Olenellus and 

 other genera of the MesonacidcC.) 



Olenellus (Hall), Lindstroim, 1901, Kongl. Svenska Vet.-Akad. Hand- 

 lingar, Vol. 34, No. 8, p. 24. (Considers Olenellus an eyeless, suture- 

 less trilobite. The discussion of the Olenellidse on pages 12-18 is al- 

 most entirely based on features exhibited by the type species of the 

 genus Elliptocephala, and a reference to those pages is therefore 

 • placed under the latter genus.) 



Genotype. — Olemis thompsoni Hall, 1859. 



The adult form of Olenellus thompsoni Hall has been described 

 and illustrated [see Walcott, 1886, p. 167, and 1891, p. 635], but 

 discoveries made since 1891 have added so much to our knowledge 

 of the younger stages of growth of some species of the genus as 

 restricted in this paper [p. 328] that a brief description of them will 

 be given. 



For convenience of reference dorsal shields from the type locality 

 at Parkers quarry, Georgia Township, Vermont, are illustrated [pi. 

 34, fig. 9 ; pi. 35, % i]. 



Olenellus has a large semicircular cephalon, elongate eyes, and the 

 anterior expanded lobe of the glabella is more or less clearly united 

 to the eye lobes by connecting ridges. The thorax has fourteen seg- 

 ments and an elongate terminal telson that is quite unlike the py- 

 gidium of any other genus of trilobites, but that is similar in appear- 

 ance to the telson of Limulus. The third segment of the thorax is 

 enlarged and extended in a strong and long pleura on each side. 



