324 Reviews — Wachsmuth ^ Springer'' s Ilonograjih on Crinoids. 



based on sound developmental principles, and conduce to a clear 

 understanding of the variations in skeletal structure presented by 

 the several Orders and Families. 



The account of the Stem (pp. 38-58) has much value, not merely as 

 a summary of known facts, but as introducing new details, and for the 

 first time using the variations of this organ as factors in the main 

 scheme of classification. The authors believe that the Crinoidea may 

 be divided into two groups in accordance with the growth of the stem. 

 In one group new columnals are developed next the cup, so that the 

 top columnal is always one of the latest formed, and continually moves 

 from its proximal position as new columnals develop. This group 

 includes all genera which the authors assign to their Orders Inadunata 

 and Camerata. In the other group the top-columnal is not the 

 latest formed, but is a persistent 'proximale' {vide p. 320). This 

 group includes the Tchthyocrinoidea of some previous classifications, 

 the Apiocrinidge, Bourgueticrinidas (including RMzocrinus), Ante- 

 donid^ and similar forms, Eugeniacrinidee, and Holopodidas; it is 

 named ' Articulata ' by Messrs. Wachsmuth and Springer, but, as 

 I have elsewhere urged. Von Zittel's name of ' Flexibilia ' is free 

 from the variety of meanings under which the word Articulata 

 labours. This grouping, according to stem-growth, is not made 

 superior to the previously existing ordinal divisions ; but so far as 

 the definition of the Order Flexibilia is concerned, it affords 

 a diagnostic character of importance. The systematist, however, 

 though he may welcome such an aid, is bound to criticize with care 

 the evidence on which it is proposed. In this case so slight is the 

 attempt at proof that scepticism remains our only attitude. A student 

 seeking a subject of research could not do better than investigate 

 this question thoroughly. 



As for the stem generally, it is obvious that a digested body of 

 information, with reference to its characters in genera and species, 

 would be of the utmost value to the stratigrapher, who finds 

 thousands of stem-fragments, at present indeterminable, to one 

 determinable crown. What are the prospects of our ever being able 

 to determine genera and species from columnals alone? Among 

 genera common in Neozoic rocks there are BMzocrinus, Bourgueticrinus, 

 Acrochordocrinits, and the Pentacriuidte, which are pretty readily 

 determinable ; while in the highly specialized Pentacrininge, at all 

 events, the details of the stem are often characteristic of species. 

 It is less easy to separate the genera and species of Encrinidee, 

 Apiocrinidse, and Eugeniacrinidas on these characters, although a 

 few are fairly distinct (e.g., Traumatocrinus, Millericrinus Iwrridns, 

 M. Charpyi). Among Palseozoic genera the differentiation of the 

 stem had as a rule not proceeded so far, but peculiar and characteristic 

 structures are presented by Barycrinus, Eerpetocrinus, the Platycrinidas 

 (sens, str.), Crotalocrinus, Cupressocrinus, and a few others. The 

 majority of Palasozoic columnals, however, are simply circular in 

 section with their joint-surfaces marked by radiating strias ; such 

 specimens are the terror of the palfeontologist. Nevertheless stem- 

 characters, even in unpromising genera, deserve careful study. In 



