No. 89.] 



127 



Among the new genera of Crinoidea, the most remarkable is the Edriocrinus; 

 which, although fixed and without pedicel in the young state, is quite free in its 

 mature condition. 



The illustrations of the Genus Platyceras of Conrad present a wide variation 

 of form and manner of growth, graduating in the difi\jrent species from closely 

 enrolled spires to a single volution at the apex ; and others are entirely free from 

 volutions, and present a slightly arching conical form. 



There are few species among the Cephalopoda, and the paucity of these forms is 

 in striking contrast to the same in the first volume. 



The species of Trilobites each represent (some of them more extravant in form) 

 those previously described from the Niagara group. 



Ptertgotus is, for the first time, recognized among American fossils; while 

 Ceratiocaris, heretofore known by a few of the caudal spines, and referred to 

 another genus, is recognized in three species in the Waterlime group. 



Of EuRTPTERUS, two American species were pj-eviously known, the E remipes 

 of Dekat and the JE. lacustris of Harlan. Mr. Hall has brought together all 

 the collections known to him in the State of New-York, and has been enabled to 

 add ( principally from the State Collection and from that of Mr. C. Cobb of Buf- 

 falo*) six new species; one of them presenting some remarkable variations, which 

 induce him to refer it to a distinct subgenus. He has also discovered and combined 

 all the parts of the animal, which has never before been done; so that we now 

 know the entire number of articulations of the body, the number and character of 

 the organs of locomotion, together with their appendages (consisting of straight 

 or curving spines), and the form and position of the mouth. The feet, of which 

 the exterior parts serve for locomotion, have their bases expanded and serrate to 

 perform the office of manducation. 



These discoveries in the peculiar Genus Eurtpterus are of the greatest interest; 

 and their publication at this time will doubtless excite attention among all ama- 

 teurs, and others who may be engaged in the collection of such remarkable fossils 

 as this and its. associated Genera Ptertgotus and Ceratiocaris. The subject of 

 these large crustaceans has recently engaged the attention of the palaeontologists 

 of the Geological Survey of Great Britain; but their results, as published at this 

 time, do not aiford the positive information regarding structure, that is here given 

 in the Palaeontology of New-York. 



These remarkable crustaceans are regarded bj'- Sir Roderick Murchison as 

 marking, in Europe, the age of the uppermost Silurian strata; and by Mr. Salter, 

 as entering into strata of well-marked Devonian age; while Mr. Hall has here 

 shown that they lie at the base of, or below, the Lower Helderberg group of rocks 

 (which are of acknowledged Silurian ago), and are separated from the earliest 

 known Devonian or fish-bearing beds by a considerable thickness of well-marked 

 Silurian strata. In England, the beds bearing Eurtpterus and Ptertgotus are 

 directl}-- below the beds containing fishes, and the fossils of the two are sometimes 

 described as mingled together. In this volume it is shown how, in the absence of 

 the Lower Helderberg group and Oriskany sandstone, the beds with remains of 

 Eurtpterus and Ptertgotus may lie directly beneath the limestones containing 

 remains of fishes; while in this country, along an outcrop of hundreds of miles, 

 the two are never known to be mingled together. 



♦ The author has likewise, in the preface to the volume, made his aoknow]cdgments to 0. 

 OsBORN, esq., and Mr. Tower, of Waterville, for specimens of Eurypterus remipes; and to 

 Col. Jewett, for the use of similar specimens. 



