230 CONTRIBUTIONS FROM 111 l NATIONAL HERBARIUM. 



ANNOTATED CATALOGUE OF GENERA AND SPECIES. 



The following k<\\ to ilif genera included in this report is offered 

 merely as an aid in identifying these genera. From a phylogenetic 

 standpoint its value is probably small. The arrangement is practi- 

 cally that of K. Schutt in Engler & Prantl's Pflanzenfamilien/ 1 the 

 changes being mainly the restoration of the earlier names of some of 

 the genera in the place of those given by Schutt. Some slight rear- 

 rangement has been found necessary, for reasons explained in the 

 text, as tlu* placing of Vanheurckia, Reicheltia, and other genera 

 under Frustulia, and the closer union of Axtinocyclus with Coscino- 

 discus. Minor changes in the wording were also required in a few 

 places. This genera] arrangement of Schutt appears more workable 

 than that of II. L. Smith, 6 on which it is partly based. They both 

 avoid the fatal difficulty of the classification of Pfitzer/ worked out 

 on the basis of chromatophores, etc., of the living cell. Although 

 Pfitzer's arrangement is of great biological value, its distinctions ire 

 m> uncertain of application to the diatoms as a class, the great majority 

 of which are know o only in .1 fossil state, t hat it can never come into 

 genera] use from a taxonomic standpoint. 



No attempt is made here to carry the classification down into the 

 separate species of the different genera. Despite tin 4 great industry 

 and ability in making keys to the species based on verbal distinct ions 

 exhibited in the monographs of Cleve, Rattray, and other diatomists, 

 the writer must confess to his inability to use these w it h any feeling of 

 security. Verbal descriptions are very valuable, but without accom- 

 panying illustrations they are rarely conclusive. The differences 

 between species being based on the varied and often immensely coin- 

 plicated sculpturing of the valves, it is almost impossible to describe 

 these differences clearly and at the same time tersely enough to serve 

 the purpose of analysis. A good photograph or drawing of a diatom 

 will always be of more value for identification than any amount of 

 word painting. As it is not practicable to accompany this report 

 with figures of all the species here enumerated, copious references are 

 given to works in which satisfactory illustrations are to be found. 



SYNOPTICAL KEY. 



Subfamily I. CENTRICAE. Valve centrally built; thai is, arranged in relation i" 

 a central poinl or focus rather than in relation to :i median Inn-: outline circular, 

 oval, or elliptical, sometimes polygonal, rarely crescent-shaped or Bpindle-shaped ; 

 neither a raphe, cryptoraphe, nor pseudoraphe present; valve-markings < - i 1 1 1 « -1- 

 concentric, radial, decussating, or irregular, never ]>iimai<'; processes (horns, 

 Bpin< 3, etc common. 



o Pflanzeniamilien, A. Engler A K. Prantl, Theil I. Abteilung L6. Leipzig, L896. 

 & Conspectus Diatomaceae, H L. Smith, The Lens 1 : 1 19,72-93, i.'.i L67. L872. 

 - Hanst. Bot. Abhand. 'S. L871. 



