526 COSCINODISCUS. 



works by Mr. Grunow, Mr. Rattray, and Mr. J. D. Cox. It will be convenient 

 to make a few remarks about each. The work of Mr. Grunow will be found 

 in his important publication Die Diatomcen von Franz Josefs Land. Mr. 

 Grunow there arranges the Coscinodiscus into two principal groups, the Radiati 

 and the Fasciculati, to which is added a third small group the Pseudo 

 stephanodisci. He admits into each group a limited number of principal 

 forms or species, to which he attaches a considerable number of varieties or 

 sub-varieties. Mr. Grunow states that the difference, the delimitation of 

 species, is extremely difficult in consequence of the innumerable transitional 

 forms which knit together the large groups. In this way is the Radiati, which 

 are characterised by the cellular structure ; in many species the cells pass into 

 puncta. Mr. Grunow's work is one of considerable importance, in which the 

 stamp of a master is clearly recognizable, and I advise anyone who desires to 

 devote himself to the Coscinodiscus, to study it thoroughly. 



Mr. Rattray has published "A revision of the genus Coschiodiscus and some 

 allied Genera," a volume of 240 pages, and a work of great importance. Mr. 

 Rattray introduces into the genus Coscinodiscus several allied genera, which 

 are easily distinguished, and which consequently deserve to be preserved, if 

 only to facilitate their determination. In any case, Mr. Rattray's work gives 

 in a condensed form all that is known of the Coscinodiscus, and it would be 

 impossible to devote oneself to this genus without recognizing the work of 

 this skilful monographist. 



The third work, which is not the least original, has been pub- 

 lished by Dr. J. D. Cox, under the title of "The Coscinodiscae ; Notes 

 on some unreliable criteria of genera and species." The Hon. J. D. 

 Cox, starting from the same point of view as many well-known diatomists, 

 deplores the immense number of forms which have been created in the genus 

 Coscitwdiscus, and he proposes to refer all the Coscinodiscus to seven forms, 

 which are as follows : 



1. Actinocyclus Ehrenbergii Ralfs. The disc is divided into 

 compartments or segments by radial lines of alveoli, at the marginal end of 

 which is a small spine. Each compartment is filled by a fascicule of lines of 

 alveoli, of which the middle line is radial and the other lines parallel to the 

 middle one. The outer rim is bevelled or curved sharply beyond the spines, 

 and upon this are more numerous lines of finer alveoli, making decussating 

 as well as radial striae. A "pseudo-nodule" is near the margin. 



2. Coscinodiscus subtilis Ehr. Marking of the disc like the last, 

 except that the radial lines between the fascicles are omitted, and the parallel 



