378 Reviews — Silurian Cnnoich of Chicago. 



suggestion ; but it remains no more than a suggestion, to be confirmed 

 or rejected when our knowledge of Sihirian faunas is far greater than 

 it now is. A remembrance of the numerous local variations in the 

 character of the Silurian faunas, and of the sporadic distribution of 

 many genera, especially among crinoids, should make us exceedingly 

 cautious. It is well, however, to keep these broad questions before 

 our minds, since they emphasize the need for the most detailed 

 systematic description and the most exact collecting. 



In view of the importance of correctness and exhaustiveness in 

 work of this nature, it may be as well to remedy a few slips and 

 omissions that have very naturally crept in, as well as to make 

 a few minor suggestions. Dr. Weller gives a Bibliography of 

 Silurian Crinoidea, believed to be nearly complete so far as American 

 literature is concerned. It does not, however, contain the names 

 of F. de Castelnau, E. J. Chapman, T. A. Conrad, B. F. Shumard, 

 E. P. Whitfield, or L. P. Yandell ; nor is there reference to 

 J. Hall's paper in Trans. Albany Institute, x, p. 57, or to Beachler's 

 notes in the American Geologist, vii, p. 178, and ix, p. 408. Reference 

 to J. W. Salter's appendix to Sutherland's "Journal," 1852, might 

 give Dr. Weller more information about Arctic American crinoids, 

 while he might be interested in a note of my own on Bracliiocrinus 

 {Amer. Geol., xvi, p. 213). Neither that genus nor its unique 

 species is mentioned in his very useful list of Silurian Crinoids, 

 which also lacks my Botryocrinus decadactylus and B. ramosus. 

 A stranger omission is that of Hapalocrinus retiarius (Phillips, as 

 Actiuocrinus). Hapalocrinus, which is due to Jaekel, is, as one 

 anticipated, confused with Haplocrinus, Steininger. Dr. Weller 

 does not, of course, intend his list as authoritative on nomenclature ; 

 but it is as well to point out that Cyathocrinus capillaris, Phillips, 

 is a Gissocrinus, that Poteriocrinus dudleyensis, Austin, is at all 

 events not a Cyatliocrinus, that Pisocrinus miJligani, Mill. & Gurl., 

 is synonymous with P. qidnquelohus, Bather, and that Pycnosaccus 

 ornatus, Weller, is apparently a lapsus calami for P. americanus, 

 Weller. I may further take this opportunity of stating that 

 Arachiocrinus, Callicriniis, Calpiocrinus, Cordylocrinus, Desmidocrinus, 

 Hapalocrinus, Lyriocrinus, Mariacrinus, Patelliocrinus, Pycnosaccus, 

 Stephanocrinus, and perhaps other genera, are represented in the 

 Wenlock Limestone or Wenlock Shale of England, although not 

 so indicated in Dr. Weller's list of genera (in some cases through 

 inadvertence). This substantiates the criticism that Dr. Weller's 

 comparative census is, through no fault of his, a little too " previous." 



The memoir contains a general account of crinoid structure which 

 should be useful to those for whom it is intended. But is it quite 

 safe to say that the food-supply of a crinoid is increased by its 

 stationary position ? The assertion seems to ignore the locomotive 

 power of those crinoids that are not attached as well as the action 

 of ciliary currents. At any rate it is misleading to describe 

 Carahocrinus as "a very simple crinoid whose dorsal cup consists 

 entirely of three circles of plates." The definition of the terms 

 ' proximal ' and ' distal ' applies only to the dorsal elements ; for 



