Raymond: Notes on Ordovician Trilobites. 67 



Ifiiiith in front of the posterior margin of the cephalon. P^ree cheeks 

 drawn out into spines which extend back to the middle of the thorax. 



Thorax of eight segments, the axial lobe slightly less than one-half the 

 total width. 



Pygidium subcircular in outline, gently convex, with a wide flattened 

 border. The axial lobe is very obscurely defined. 



The best specimen was, when entire, about 50 mm. long. The pygidium 

 is 18 mm. long and 22 mm. wide; the thorax 16 mm. long and the median 

 lobe is a little less than one-half the total width (.45). A larger pygidium 

 in the Carnegie IMuseuin is \(^ inni. long and 52 mm. wide. 



This species differs from Isotcliis gigas in having a subcircular instead 

 of a subtriangular pygidium, and in having longer genal spines. In some 

 ways it is like Isoteloides ivhitfieldi of the Beekmantown, but the axial 

 lobe is wider, the cephalon lacks the median tubercle, and the glabella 

 is not defined as in that species. 



Locality. — This species occurs in the buff dolomite of the reefs at the 

 base of the Upper Chazy on V'alcour Island, New York, and on Isle La 

 Motte, \'ermont. The mould of the nearly complete specimen is in the 

 collection of the Geological Survey of Vermont, and the large pygidium 

 figure is in the Carnegie Museum. 



Isotelus beta Raymond. 



Plate XIX, figures 4-7. 

 Asaphus beta R.wmond, Annals Carnegie Museum, III, 1905, 342, pi. 12, fig. 9. 



The little pygidia called Asaphus beta in my previous paper are very 

 abundant at McCuUough's sugar bush at Chazy, and are there associated 

 with cranidia and free cheeks of an Isotelus of corresponding size. These 

 little trilobites agree with Isotelus harrisi in having the eyes rather far 

 forward, but the cranidium is not so short and wide as in that species. 

 The pygidia are less broadly bordered and the genal spines are shorter 

 and less flattened than in Isotelus platymarginatus. The name beta is 

 therefore retained for the present. The thorax is unknown. 



Genus Isoteloides Raymond. 

 This genus was proposed in a previous article in this number of these 

 Annals for trilobites with the smooth form and concave borders of 

 Isotelus but with a narrower axial lobe, a somewhat definitely defined 

 glabella, and an Asaphus-WkG. hypostoma. The type is Asaphus canalis 

 as described by Whitfield {Isoteloides whitfieldi Raymond). Isoteloides 



