122 PALEONTOLOGY OF NEW YORK. 



annulation of the pygidium. The surface of the hypostoma is punctate and 

 covered with strong, concentric, lamellose markings. 



Dimensions. An average individual affords the following measurement: 



Body. Cephalon. Thorax. Pygidium. 



Length 36 mm. 14 mm. 12 mm. 10 mm. 



Width 22 mm. 22 mm. 20 mm. 18 mm. 



The smallest entire specimen observed has a length of 12 mm., and a 

 width of 9 mm., and the largest specimen, in which the parts are somewhat 

 detached, was an individual measuring 62 mm. in length. 



Observations., Proitus Rowi is one of the rarer species of the Hamilton fauna. 

 The fossil was first brought to public notice by Mr. Le Row, in the Poughkeepsie 

 Telegraph of November 22, 1837, and was described by Green in the following 

 year, as cited. The original was from the sandy shales of the group in Otsego 

 county. In one locality only has it proven to be an abundant fossil in good 

 preservation, namely, on Seaver's creek in the township of Canandaigua, Ontario 

 county, in the shales and limestone immediately overlying the Marcellus shales. 



Careful comparison of this species with Proi'lus clarus, Hall, of the Upper 

 Heidelberg limestone, shows a very close similarity in the broader features and 

 in the general expression of the animal. While the former may be regarded as 

 the Hamilton representative or descendant of the latter, there are certain asso- 

 ciate! details which will serve to distinguish the species. Proitus Rowi has larger 

 eyes, flatter thoracic segments, a less abruptly tapering axis and a larger num- 

 ber of annulations upon the pygidium, and a peculiar ornamentation upon the 

 cheeks, thorax and pygidium, which has not been noticed in Proitus clarus. 



Proitus marginalis. 



Calymem marginalis, Conrad. Ann. Rept. Palaeontology of N. Y., p. 66. 1S39. 



Proitus marginalis ('.). Mall. Descr. New Species of Fossils, etc., p. 76. 1861. 



Proitus marginalis (?), Hall. Fifteenth Rept. N. Y. State Cab. Nat. Hist., p. 104. 1862. 



Proitus marginalis (1), Hall. Illustrations of Devonian Fossils, pi. xxi, figs. 24-28. 1S76. 



The original of Mr. Conrad's Calymene marginalis was a cephalon described 

 by him in the following terms {loc. cil.) : 



