JVaviculacea.] infusorial animalcules. 309 



permanent arrangement can be made according to their affinities. 

 The improvements on the microscope have enabled us to discover 

 markings on the shells previously considered smooth, hence new 

 divisions are daily required. In the following pages the plan of the 

 former edition will be continued, so far as to form them into three 

 sub-sections, \iz., JS^aviculece, EchineUce and Lacernatm. In each of 

 these the genera will be placed in. alphabetical order, but when a 

 large genus has been divided, its members, or sub-genera, will be 

 found with it. Eefcrcnce to the index will afford every facility 

 required. (This section is illustrated by P. 2, 3, and 4, f. 127 to 208. 

 P. 13, f. 45 to 50. P. 14 to 20 and 24, except a few figures in 

 plates 14, 15 and 18.) 



Sub-section. — NAVICULE^ (Navicuiacea Liatomece.) — Lorica 

 simple, unattached. 



Genus AcTiNocrcLrs. (Ehr.) — The rayed hox-lihe leings ; bivalve, 

 disciform, or shortly cylindrical, cellular f reticulated j ; the cells 

 interrupted by many smooth rays ; self-division imperfect, forming 

 chains ; lorica Avith internal septa. Kiitzing, however, characterizes 

 the members of the genus as solitary, and, moreover, as destitute of 

 internal septa. 



Ehrenberg observes, that the cellular character of the lorica, dis- 

 tinguishes Actinocyclus from Gallionella, although an approach to 

 a like condition may be seen in Gallionella sulcata. 



Actinocyclus, Actinoptyclius, and Coscinodiscus, constitute Kvitzing's 

 family Coscinodiscem. This family is most akin to Melosira f Gallionella, 

 Ehr.) but differs by the cellular or reticulated surface of the discs. 

 AH the genera are marine. 



A very large number of species of Actinocyclus have been created 

 by Ehrenberg, the characteristics of which he derived from the 

 number of rays, and where this failed, from the presence or ab- 

 sence of septa. Of the latter plan, the distinction between 

 A. bioctonarius and A. sedenarius is an example, the number of 

 rays being alike in the two ; but the former is destitute of septa, 

 which the latter possesses. More recently, Ehrenberg has created 



