876 INFUSORIAL ANIMALCULES. {Poli/ffagirica. 



frustules in pairs, each with a strongly-marked central line (suture.) 

 On marine Algae, Torquay, Hastings, &c. 



" Melosika Borreri (Greville.) — Frustules rather longer than broad, 

 cylindrical, rounded at the ends, with a centi'al strongly-marked line 

 (suture of the valves, Ehr.) Marine Algae." 



This species much resembles M. nummuloides ; the filaments are 

 stouter, the ends less convex, and marked only with a central line. 



" 'K. arenaria {'hiooxe.) — Filaments stout, frustules broader than 

 long, with a single central line; junction-surfaces closely united, 

 striated. Fresh water ; brownish when recent ; pale green when dried. 



"Filaments much stouter than in any other species, distinct to the 

 naked eye ; when rubbed between the fingers, feeling rough like 

 givains of sand, whence its specific name. The junction of the 

 frustules appears like a dentated surface. (See f. 131 and 199.) 

 The characters by which this species is distinguished from M. varians 

 have been so clearly pointed out by Mr. Dalrymples, that I shall use 

 an extract from his letter, instead of making any observations of my 

 own." 



"JJelosira r an'mis (^Agardh) is as clearly GaUionella varians, asMelosira 

 areymria (Moore) is OaJlionella varians, (Ehr.) — Still no tyro in 

 Natural History could presume, thtt the two were the same species. 

 The characteristic difference exists in the well-marked feature of the 

 striae at the junction-line of the corpuscles, and which, combined 

 with their discoid form, bears a strong resemblance to the milled 

 heads of many of the adjusting screws of our microscopes. Added 

 to this, is the appearance of radiating lines, seen when the flat sur- 

 face of the disc is ia view." 



M. varians (Ralfs.) — Frustules once-and-a-half to twice as long 

 as broad, with a single central line ; the ends slightly rounded ; junc- 

 tion-surfaces without striae ; filaments very slendci", but varying much 

 in thickness ; fragile. Brownish when recent ; becomes green on 

 drying. In fresh water rivulets, and ditches. 



The end being rounded, the joints are not so closely united as in 

 M. arenaria and M. aurichalcea. Not unfrequently, this species has 

 the joints dilated here and there into a globular form ; and in this 

 state the central furrow gives the appearance of two joints com- 

 bining in the formation of the inflated cells (P. 24, f. 32.) 



