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 successor in the Lower Helderberg, _H. Vanuxemi_, which, according to the restoration from a very large fragment given in the Palæontology of New York, Volume VII (plate V B) grew to a length of at least 11½ inches. SALTER has mentioned (Palæontographical Society, vol. xvii, p. 109) a large fragment of _Homalonotus 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. BRUSHAUSEN 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. Unquestionably the largest individual of HOMALONOTUS known is that of _H. major_, from the Oriskany sandstone, figured in the Palæontology 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 been well nigh 15 inches. The later and common Hamilton species, _H. DeKayi_, attained no extravagant size though frequently large, e. g. the enrolled individual figured on plate IV (_op. cit._), the largest entire specimen reported, which is about 9 inches in length; some large fragments indicate that the animal was sometimes as long as 11 inches. The size attained by some of the Devonian species of DALMANITES and their immediate predecessors was marvelous. The pygidium of _D. micrurus_ figured in the Palæontology of New York, Volume III, page 359 (there given as _D. pleuroptyx_), indicates an individual at least 11 inches in length, and there is reason to believe that the Lower Helderberg species, _D. nasutus_ and _D. tridens_, attained a size fully as great. Most remarkable however is the great pygidium of _D. myrmecophorus_ of the Corniferous limestone, figured upon plate XV of Volume VII (_op. cit._), which from the restoration there given, made from careful comparative measurements, would imply an individual 16 inches long.