long and 12 inches broad." This is an evidently much compressed 

 fragment, measuring seven inches in its greatest transverse diameter, 

 and assuming this as the greatest diameter of the pygidium and 

 restoring the length from the proportions of the animal as there 

 given, the original length of its owner would have been about 13 

 inches. The plate is incomplete on its anterior portion, and it is 

 probable that the error in this estimate due to the exaggeration of 

 size from compression of the shield, is compensated by the loss of 

 diameter from imperfect retention. This great pygidium, with other 

 large fragments of the same species, were used as a basis for a well- 

 known restoration in plaster to be found in some of the older muse- 

 ums of this country. Angelin has given a restoration of Megalaspis 

 heros 14 inches in length and Brogger estimated the original length of 

 Megalaspis acuticauda to be fully 16 inches. Barrande figured an 

 entire Asaphus nobilis from Etage D which measures 10| inches. 



Not until the introduction of the genera Dalmanites, Homalonotus 

 and LicHAS do we meet with the most gigantic proportions attained 

 by these crustaceans, and then only after these genera have become 

 well established. Perhaps none of their representatives in the lower 

 Silurian faunas were of commanding size ; in the upper Silurian large 

 but not extravagant proportions were sometimes attained. Lichas 

 Boltoni of the Niagara fauna, is a magnificent species, one of the 

 largest of its race and remarkable for the frequency with which its 

 parts are found together, an extremely uncommon occurrence in this 

 thin-shelled group. The Lichas pustulosus of the Lower Helderberg 

 shaly limestone was a great species attaining a length of 10 inches or 

 more. Homalonotus delphinocephalus of the Niagara fauna grew to 

 large size but does not appear to have attained the length of its suc- 

 cessor in the Lower Helderberg, H. Vanuxemi, which, according to the 

 restoration from a very large fragment given in the Palaeontology of 

 New York, Volume VII (plate V B) grew to a length of at least 1]| 

 inches. Salter has mentioned (Palseontographical Society, vol. xvii, 

 p. 109) a large fragment of Homalonatus rudis which he estimates may 

 have been a foot in length. In later faunas are found traces of this 

 genus of still greater size. Dr. Beushausen has figured a pygidium of 

 H. gigas from the Spiriferen-sandstein of the Hartz, the possessor of 

 which must have been upward of one foot in length. Unquestion- 

 ably the largest individual of Homalonotus known is that of H. major, 

 from the Oriskany sandstone, figured in the Palaeontology of New 

 York, Volume VII (plate V A), a large fragment representing the 

 greater part of the thorax and the pygidium, and according to the 

 restoration there given the original length of the animal must have 



