FKOM NORTH AMERICA, WALES, AND IRELAND. 23 



broad furrowed notch in the Devonian Ki/amodes Whidhornei, Ann. 

 & Mag. N. H. ser. 6, vol. ii. 1888, p. 296, pi. xi. 



The valves have a bright surface ; thej are in the same black 

 rock as that containing Isochilina cristata. These two have their 

 representatives in the Lower-Silurian rocks of Canada, which supplied 

 Isochilina gracilis and /. Ottaiua, Ann. & Mag. X. H, ser. 3, vol. i. 

 1858, p. 248. 



Isochilina gregaria is closely allied to Isochilina grandis^ Jones, 

 Ann. & Mag. N. H. ser. 2, vol. xvii. 1856, pi. vii. fig. 14, and 

 op. cit. ser. 5, vol. ix. 1882, p. 171. 



In hard black calcareous shale, Cave Island, Ball's Bay, Lake 

 Charaplain, Vermont. Probably from the Calciferous-Sandstone 

 Formation. 



5. Isochilina cristata (Whitfield). (PI. I. fig. 8.) 



Primitia^ cristata, Whitfield, ' Bulletin Amer. Mus. N. II.' vol. ii. 

 no. 2, 1889, p. 59, pi. xiii. figs. 1 & 2. 



Size : length 2-8 mm., height 1*8 mm. 



The specimen here figured differs somewhat in outline from either 

 fig. 1 or fig. 2 of Prof. Whitfield's memoir ; it has a more simple 

 nuchal depression without any tubercles, and shows a non-punctate 

 surface. The nuchal mark varies in intensity in diff'erent specimens. 

 The short, oblique ridge below the centre is always present. 



This also is an Isochilina, there being no ventral overlap ; other- 

 wise it might well be a Leperditia. From Cave Island, as above. 



For the three foregoing species of Isochilina, characteristic speci- 

 mens were chosen and drawn betore the Memoir by Prof. II. P. 

 Whitfield came to hand. 



6. Isochilina ?, sp. (PI. I. fig. 15.) 



Size : length 4*1 (?) mm., height 2-3 (?) mm. 



In fig. 15 we have indications of a Leperditioid valve with a 

 nuchal depression as in tig. 8, and a broken, hollow, subcentral 

 process, analogous to the oblique ridge in fig. 8, but apparently 

 stronger and more limited in area. It may, however, have been 

 more like the sharp process in Kolmodin's Leperditia tuherculata, 

 (Efvers. k. Vet.-Akad. Forh. (1879), 1880, p. 135, pi. xix. figs. 1 a, 

 1 b ; and Walcott's Leperditia (Isochilina) armata, ' Thirty-fifth 

 Keport N.Y. State Mus. N. H.' 1883, p. 213, pi. xvii. fig. 10. 



From Cave Island, as above. 



X. Genus Leperditia, Eouault, 1851. 

 1. Leperditia (?) seneca, Hall. (PI. I. figs. 13, 14.) 



Leperditia seneca. Hall, ' Fifteenth Annual Report, University of 

 the State of New York,' 1862, p. 112. 



^ize{^^- 



Size^^'^-}^ 



Length, 



Height. 



uim. 



nun. 



•62 



•44 



•56 



•36 



