220 DESCRIPTION OF [Polygastrica. 



square, and marked with continuous longitudinal lines, but 

 not with transverse striae. Found upon Ceramium rubrum. 

 Length 1 -430th. 



290. Tessella interrupta is nearly square, with the 

 longitudinal lines interrupted in the middle ; striae none. 

 Length of table l-570th. 



Genus LXIII. Fragilauia. The fragile little wand 

 Animalcules comprehend free Infusoria, inclosed in a 

 simple bivalved or multivalved siliceous lorica, prismatic 

 in form, resembling Navicula. Self-division, both of lorica 

 and body, incomplete ; hence they are in the form of band- 

 like chains, and are very fragile. In most species each end 

 of the lorica has two openings ; these are in the same 

 plane, so that the surfaces upon which the chain rests 

 may be considered lateral, and the self-division will then 

 be dorsal. The whole chain sometimes rises in the water 

 and turns itself round, while simple specimens have a 

 progressive movement. In F. grandis, turgidula, scalaris, 

 diopthalma, and pectinalis, polygastric stomach-cells are 

 seen. The ova clusters are green or yellowish, when 

 young, but reddish-brown when old. The most evident 

 manner of propagation is dorsal self- division. In many 

 species the creature continues to grow both during and 

 after self- division, but in F. striatula increase of size ceases 

 after division. 



291. Fragilaria grandis. The great Fragilaria is 

 striated, lanceolate in form, the ends obtuse laterally. 

 As many as thirty often cluster in a single band. Fig. 171 

 is a band of seven ; in four of them the ova protrudes, 

 a portion of the lorica being cut oif. In 1-lOOth of a line 

 there are eleven striae. Found in fresh water. Bands 



