Bacillaria.'] infusorial animalcules, 227 



The primaiy divisiou of Bacillaria, adopted by Ehrenborg, uud 

 based on the circumstance of the presence or absence of a gelatinous 

 indu-sdum about or upon the true lorica) or frastules is faidty, inas- 

 much as this gelatinous envelope is met wdth in various Besmidiacea 

 and Namculacea in the adidt state, and generally in all forms during 

 the process of conjugation, as a temporaiy production. "Where, 

 however, the gelatinous mass plays a more important part, forms a 

 nidus (matrix) for very numerous frustules, and is built up in a cer- 

 tain, defixdte manner, producing a chai'acteristic thallus — expanded 

 frond, it waiTants the separation of such compound organisms from 

 solitary, or merely concatenated forms, and their grouping together 

 as a subsection. 



The distribution of those Bacillaria, having a ' simple loriea,' into 

 three groups, as made by Ehrenberg (see table page) is not generally 

 followed : for most naturalists are indisposed to assign so high a 

 distinctive value to the fact of the attachment of the loricee, as is 

 done by Ehrenberg, in the construction of the group Echinellea. 

 Indeed the attachment of a frustule, or chain of fi-ustules, appears 

 inconstant, and several of the genera enumerated by Ehrenberg as 

 free, subsequent obsei-vations have proved to occxu- also attached. 



The prevailing plan is to make two sections, or families : viz., 

 1. Besmidiacea or Besmidiecs. 2. NavicuJacea; the latter including 

 the EcliimUea, and the organisms with a double * loriea' the Bacernata 

 of Ehrenberg. 



The Naviculacea are sometimes called, Biatomacea, Biatomece, and 

 CymheUece. 



Mr. Harvey, in his Manual of British Marine Algoe, considers the 

 Biatomacea and Besmidiacea as well marked sub-orders, or proper 

 orders of a common alliance — the Chlorospermece, or green Algae. 

 Mr. Ralfs considers that the Besmtdiece can no longer be united with 

 the Biatomece in one family — and gives the follomng distinctions : 

 " The cell in the Besmidiece consists of two valves united by a central 

 suture, and, during division, the new formed portions are interposed 

 between these valves. The Besmidiece are membranous, or should a 

 few species contain silica, it is not present in sufficient quantity to 

 interfere with their flexibility. They rarely have acute angles, and 

 are seldom (if ever) rectangular. They are often deeply incised or 



