484 ANIMAL NATURE OF DIATOME^. 



like condition exists in both with respect to the delicate 

 points on the shield, which Kiitzing says he has omitted 

 in his figure of Odontella; these being absolutely re- 

 ferable to the internal substance, as in the Melosirce. 



67. BiDDTJLPHiA. — Individua concafenata, punctata- 

 cellulosa {cetlulis in tineas rectas transversales ordinatis), 

 utroque latere obtuse dentata {dentiius marginalihus majo- 

 ribus) septis transversalibus internis loculosa. 



The inner cavity is not divided into distinct transverse 

 cells, because the septa, far from being complete, only 

 project in a very little way. Their greatest prominence 

 corresponds with the extremities of the frustule, and 

 thence they proceed, growing more slender, towards the 

 margins of the lateral valves, to which they exclusively 

 belong. A similar elevated rim {orlo) in the internal 

 cavity limits, also, the lateral processes by which the 

 frustules are connected together. Each of these processes 

 terminates in an acute corner {spigold), and has there- 

 fore a three-sided figure, and is situated obliquely. 



The terminal surfaces (lateral in respect to the chain) 

 are smooth, or they present an elliptico-elongate figure, 

 traversed, parallel to the smaller axis, by two lines which 

 mark the conjunction of the two lateral valves with the 

 median body. Corresponding externally to these lines, 

 is a deep furrow, which is clearly seen in the projecting 

 corners {spigoli) ; internally there is a projecting fold 

 {cercine), like an incomplete diaphragm of the areolar 

 border. Hence the form of the frustules is very different 

 from that indicated by Kiitzing, who represents them as 

 flattened cylindroids. Por they are almost parallelo- 

 pipeds, and when they are united together by an external 

 siliceous cellular membrane, more or less incompletely 

 persistent, they constitute a prismatico-quadrangular 

 filament. When they are free, the extremities are 

 thinned, rounded, and lobed, according to the number of 

 incomplete cells. The two primary surfaces are smooth ; 

 they present transverse elevations and depressions in 



