Triloi!Itks ok riii. Chazv Limf.sionk. .34o 



Localitx. — The specimen is from the south end of Valcour Island 

 just east of the pebble beach. The specimens from which the last 

 three descriptions were drawn are in the writer's collection. 



Subgenus Isotelus DeKay. 

 Isotelus harrisi sp. nov. " (Plate 12, figures 3-7.) 



('L hvtehis laualis Mall, 1S47, Palcc>nlology, New ^'ork, volume I, page 25, plate 

 4 bis, figures 17, iS, 19. 



A large Asupluis, typical of DeKay 's subgenus Jsotcliis is of fairly 

 common occurrence throughout the Chazy, and it has been variously 

 identified as Asapliiis g(i:;'(is DeKay, Asapliits canalis Conrad and 

 Asaphus canalis Billings. Separate pygidia are not easily distinguished 

 from the pygidia of Isotelus ^^i}:;as, but the cephalon is much more 

 depressed than is usual in that species, and all the Chazy specimens, 

 even those six to nine inches long, show a strong genal spine. This 

 would make it fall in with Isotelus uiaximus Locke, but, as has already 

 been pointed out by Clarke, that species may represent only a phase 

 in the development of Isotelus i^igas. It seems probable that the 

 Chazy form is a distinct species, ancestral to Isotelus gigas, showing 

 its more primitive position in the phylogeny of the race by its reten- 

 tion of the genal spines as an adult character. 



With Asaphus canalis, as defined by Whitfield, the present species 

 does not agree, the pygidia being very different in the two species. 

 The hypostoma figured on page 270, figure 255, of the Paleozoic Fos- 

 sils of Canada as that of Asaphus canalis ? somewhat resembles the 

 hypostoma of our species, but the specimen figured on page 352, 

 figure 340, of the same work, is evidently very different both from our 

 species and from Asaphus canalis Whitfield. 



The species identified by Clarke in the Paleontology of Minnesota, 

 volume 3, part 2, page 707, figure 9, as Asaphus canalis ? Whitfield 

 also differs from the Chazy species and from Whitfield's Fort Cassin 

 specimens. Since Conrad's specific description was never published, 

 and the specimens figured by Hall under that name were so fragmentary 

 as to be indeterminable, Whitfield is the first to describe and figure a 

 specimen definitely a.?, Asaphus canalis. Asaphus canalis Whitfield, is 

 so far as known, confined to the Peekmantown formation and probably 

 to the Champlain Valley, where it may be collected at Fort Cassin, 

 Fort Ticonderoga, and Crown Point. 



