ISOTELUS. 39 



Desiring to know more of this individual, I wrote to Doctor Bather and was surprised 

 to learn that the specimen which was the basis of Woodward's observations is so badly pre- 

 served as to be of no real value. With his permission, I append a note made by Doctor 

 Bather some years ago when selecting fossils to be placed on exhibition: 



Asaphus gigas Dekay. Ordovician, Trenton Limestone. N. America, Canada. Descr. H. Woodward, 

 1870, Q. J. G. S., XXVI, pp. 486-488, text fig. I, as Asaphus platycephalus. Coll. and presd. J. J. Bigsby, 

 1851. Regd. I 14431. 



This specimen is in the Brit. Mus. Geol. Dept. I 14431. The supposed hypostome is exceedingly doubt- 

 ful; it lies dorsad of the crushed glabellar skeleton. The "appendage" is merely the edge of a part in the 

 head-shield; the maxilla is some calcite filling, between two such laminae. 



13 Sept. 1911. (Signed) F. A. BATHER. 



Walcott figured a slice of Isotelus gigas from Trenton Falls, New York, which shows 

 a few fragments of appendages, but is of particular importance because it shows the pres- 

 ence of well developed appendifers beneath the axial lobe. 



Isotelus arenicola Raymond. 

 Illustrated: Ottawa Nat, vol. 24, 1910, p. 129, pi. 2, fig. 5. 



The following quotations from my paper are inserted here to complete the record of 

 appendage-bearing specimens : 



A rather remarkable specimen of this species was found by W. C. King, Esq., on the shore of Lake 

 Deschenes at Britannia [near Ottawa, Ontario]. This specimen is an impression of the lower surface of 

 the trilobite, and shows a longitudinal ridge corresponding to the central furrow along the axis of the ventral 

 side of the animal, ten pairs of transverse furrows, and the impression of the hypostoma. The doublure of 

 the pygidium has also left a wide smooth impression, but in the cephalic region the hypostoma is the only 

 portion of which there are any traces remaining. The specimen was found on a waterworn surface of the 

 beach, partially covered by shingle. . . . 



The transverse furrows are the impressions left by the gnathobases of the basal joints of the legs. They 

 were evidently long and very heavy, but the specimen has been so abraded that all details are obscured. 

 The first six pairs of impressions are longer and deeper than the four behind. The first eight pairs seem 

 to pertain to the thoracic appendages, while the last two belong to the pygidium. From the posterior tips 

 of the hypostoma to the first gnathobases of which traces are present there is a distance of about 22 mm. 

 without impressions. In Isotelus gigas the hypostoma normally extends back to the posterior margin of the 

 cephalon, so that it seems that in this specimen the impressions of the first two pairs of gnathobases under 

 the thorax may not have been preserved. In that case, the six pairs of strong impressions may represent 

 the last six pairs of thoracic segments, and the pygidium might begin with the first of the fainter ones. 



Horizon and locality: From the sandstone near the base of the Aylmer (Upper Chazy) 

 formation at Britannia, west of Ottawa, Ontario. Specimen in the Victoria Memorial Mu- 

 seum, Geological Survey of Canada, Ottawa. 



THE APPENDAGES OF TRIARTHRUS. 



Triarthrus becki Green. 



(Pis. 1-5; pi. 6, figs. 1-3; text figs, i, 10, n, 33, 42.) 

 (Also see Part IV.) 



Illustrated: Matthew, Amer. Jour. Sci., vol. 46, 1893, pi. I, figs. 1-7; Trans. N. Y. Acad. Sci., vol. 12, 

 pi. 8, figs. 1-7. Beecher, Amer. Jour. Sci., vol. 46, 1893, text figs. 1-3; Amer. Geol., vol. 13, 1894, pi. 3; 

 Amer. Jour. Sci., vol. 47, pi. 7, text fig. I ; Amer. Geol., vol. 15, 1895, pis. 4, 5; Ibid., vol. 16, 1895, pi. 8, 



