OLENELLUS AND OTHER GENERA OF MESONACID^ 269 



Observations. — Elliptoccpiiala appears to be a more advanced form 

 of the Mesonacidas than Mesouacis. It has seven less segments in 

 the thorax and the stage of large third segment is passed in the 

 young and is lost in the adult. The five small posterior segments 

 of EUiptocephala suggest that they are rudimentary segments by 

 reversion, as in Pccdeumias [pi. 33], and not rudimentary as the 

 result of non-development, as in Nevadia [pi. 23]. From its strati- 

 graphic position and associated fossils it is probably somewhat older 

 than Mesouacis vermonfana Hall. 



ELLIPTOCEPHALA ASAPHOIDES Emmons 



Plate 24, Figs, i-io; Plate 25, Figs. 1-18 



EUiptocephala asaphoides Emmons, 1844, Taconic System, p. 21, figs, i, 2, 

 and 3. (Characterized in description of figure i.) 



EUiptocephala asaphoides Emmons, 1846, Nat. Hist. New York, Agricul- 

 ture, Vol. I, p. 65, figs. I, 2, and 3. (Copy of preceding reference.) 



Olcnus asaphoides (Emmons), Hall, 1847, Nat. Hist. New York, Paleon- 

 tology, Vol. I, pp. 256-257, pi. 6y, figs. 2a-c. (Describes species and 

 redraws the three specimens illustrated by Emmons [1844, p. 21, figs. 

 I, 2, and 3I.) 



Olenus asaphoides (Emmons), Fitch, 1849, Trans. New York State Agric. 

 Soc. for 1849, p. 865. (Occurrence mentioned.) 



Eliptocephalus asaphoides Emmons, 1849. Proc. American Assoc. Adv. 

 Sci., First Meeting, p. 18. (Discussed with particular reference to the 

 generic distinction between Eliptocephalus, Paradoxides, and Olenus.) 



Eliptocephalus asaphoides Emmons, 1855, American Geology, Vol. i, pt. 2, 

 p. 114, figs. I, 2, and 3; and pl. i, fig. 18. (Described. Figures i, 2, 

 and 3 are copied from Emmons, 1844, figs, i, 2, and 3, p. 21.) 



Not Paradoxides asaphoides Emmons, i860, p. 87 = Olenelhts thompsoni. 



Not Paradoxides macrocephalus Emmons, i860, fig. 70, p. 88, and p. 280 ^= 

 Olenellus thompsoni. (In the first edition of the Manual of Geology 

 this figure was labeled Paradoxides hrachycephalus.) 



Not Eliptocephalus (Paradoxides) asaphoides Emmons, i860, p. 280 := 

 Olenellus thompsoni. 



Paradoxides asaphoides (Emmons), Barrande, 1861, Bull. Soc. Geo!, de 

 France, 2d ser., Vol. 18, pp. 273-276, pl. 5, figs. 4 and 5. (Translates 

 into French the legend of figures i and 2 of Emmons [1844, p. 21] and 

 copies figure i of the same paper in fig. 4, pl. 5. Figure 5 of Barrande's 

 paper is copied from Emmons [1855. pl. i, fig. 18I. Barrande also 

 translates into French the description and discussion given by Hall 

 [1847, p. 256].) 



Not Paradoxides macrocephalus Barrande, 1861, Idem, pl. 5, fig. 7 = 

 Olenellus tliompsoni. 



Vermont formation." This is apparently the first use of the term " Greenwich 

 slate," the previous mention of the series, to which Mr. Dale refers on page 50 

 being the table opposite page 178 of his paper in the igth Annual Report of the 

 U. S. Geological Survey [1899! where no formation names are used. 



