no. 1046. REVISION OF BEYRICHIIDJE—VLRICH AND BA88LER. 3Q5 



median one, and, furthermore, tends to merge with the post-dorsal 

 node. 



The type of the genus Klcedenia, K. wilckensiana, occupies an inter- 

 mediate position between two sections into which the genus is 

 divisible. One of these sections, the smaller, includes, with the geno- 

 type, most of the European species, while all the known American 

 forms fall into the second. ' The first section is characterized by a 

 tendency to produce and to attenuate the anterior extremity and to 

 develop on this part one or two accessory furrows. In consequence 

 the outline of the valves is more or less triangular and comparatively 

 elongate. In the American section of the genus the valves are usually 

 shorter, the ends approximately equal and the anterior one without 

 distinct furrows. 



Of American species, K. oculina (Hall) and K. notata (Hall) 

 probably are to be regarded as nearest to K. wilckensiana. It is cer- 

 tain at least that they are congeneric, and it seems no less a fact that 

 these species belong to the same genus as those constituting the pre- 

 vailing American type of Beyrichiida? found in the late Silurian 

 Manlius and Coeymans, members of Hall's Lower Helderberg group. 

 The writers therefore feel little hesitancy in revising and restricting 

 the genus as indicated above. The elimination of the K. pennsyl- 

 vanica group is the most important departure from Jones's later 

 conception of Klcedenia. Another is the inclusion of certain species, 

 like K. tuberculata (Salter), which he had left with Beyrichia, 

 indeed, in the case mentioned, as a variety of B. klcedeni. Speaking 

 of A', tuberculata, it is worth noting that this is one of the very few 

 European Beyrichiidae that is represented in America by a form so 

 nearly like Scandinavian specimens that a specific distinction is 

 scarcely justified. Hall called the American variety Beyrichia 

 granulata. 



Except the two Ordovician species, A", pranuntia, new species, 

 and A', initialis, and the Chemung species, A', simplex, all of which, 

 though doubtless possessing the essential features of the genus, are 

 yet referred here with some misgivings, the genus Klcedenia is eon- 

 fined to Silurian rocks. In its typical expression, indeed, the genus 

 might be regarded as one of the most characteristic fossils of this sys- 

 tem. In America there are numerous, in part undescribed species. 

 By far the greater number of these are found in the upper parts of 

 the Silurian and principally in the Manlius and Coeymans lime- 

 stones. So far none has been seen in the overlying Xew Scotland 

 formation. It is interesting and important to note further that all 

 the known species are confined to Appalachian and more eastern 

 Atlantic provinces, the genus apparently having failed to gain a 

 foothold in the interior Ohioan Province. 



The new species figured on Plate XXXVIII are only a part of 

 those determined during the course of the present studies. 

 Proc. N. M. vol. xxxv— 08 20 



