OLENELLUS AND OTHER GENERA OF MESONACID.E 305 



PAEDEUMIAS TRANSITANS, new species 



Plate 24, Fig. 12; Plate 25, Figs. 19-22; Plate 32, Figs. 1-13; Plate t,;^. Figs. 

 1-5; Plate 34. Figs. 1-8; Plate 44, Fig. 7 



? Paradoxidcs thompsoni Billings [not (Hall)], 1861, Geol. Survey 

 Canada. Paleozoic Fossils, p. 11. (Mentions presence of a head repre- 

 senting Oleuellus thompsoni at Anse au Loup. In view of the 

 similarity between the heads of that species and Paedeumias transitans. 

 and the fact that Paedeumias transitans has been identified from this 

 locality in material loaned to me by the Geological Survey of Canada 

 it is probable that the latter species is the one referred to by Mr. 

 Billings.) 



? Barrandia vcrmontana Hall (in part), 1861, Report on the Geology of 

 Vermont, Vol. i, p. 370, first 6 paragraphs. (Copies the paragraph 

 given by Hall [i860, p. 117I and describes the species. The text in- 

 cludes reference to figures [see Hall, 1862, pi. 13, figs. 4 and 5 in 

 following reference] now placed under Paedeumias transitans.) 



? Barrandia vermontana Hall (in part), 1862, Report on the Geology of 

 Vermont, Vol. 2. pi. 13. figs. 4 and 5 (not fig. 2 which is a true Meso- 

 nacis vermontana) . (As stated under this reference in the synonomy 

 of Mesonacis vermontana. the specimens represented by figures 4 and 

 5 appear to be more closely allied to Paedeumias transitans than to 

 Mesonacis vermontana. ) 



? Olenellus thompsoni Billings [not (Hall)], 1865, Geol. Survey Canada, 

 Paleozoic Fossils, Vol. i, p. 11. (Reprinted from Billings, i86ia, p. 

 II. substituting Olenellus for Parado.vides.) 



Olenellus thompsoni Whitfield [not (Hall)], 1884, Bull. American Mus. 

 Nat. Hist., Vol. i, No. 5, pp. 151-153, pi. 15, fig. i. (Described and 

 discussed.) 



Olenellus vermontana Whitfield [not (Hall)], 1884, Idem, pp. 152-153, 

 pi. IS, figs. 2-4. (Discussed.) 



? Olenellus thompsoni ? Weller [not (Hall)], 1900, Ann. Rept. Geol. 

 Survey New Jersey for 1899, pp. 49-51, pi. i, figs. 9-10. (Described and 

 discussed. Only the head of this species is figured but it appears to 

 be referable to Paedeumias transitans.) 



In 1892 Prof, Atreus Wanner, of York, Pennsylvania, called my 

 attention to the presence of well-preserved specimens of what we 

 considered to be Olenellus thompsoni (Hall) in argillaceous shales at 

 York [Walcott, 1896, pp. 13 and 16, footnote]. Subsequently Dr. 

 Charles Schuchert made a large collection for the National Museum 

 from the localities discovered by Professor Wanner, and later the 

 latter permitted me to study the material in his private collection, 

 and recently sent a number of well-preserved specimens of the 

 younger stages of growth that he had found during the past ten 

 years. The study of all available material has resulted in discover- 

 ing a curious and interesting series of changes between the protaspis 



