ANIMAL NATURE OF DIATOME.E. 401 



systematico) has not gone the length of separating them 

 from the other species with which in all other respects they 

 have superior affinity. And as to the transverse striae, 

 this character of their interruption at the median line, 

 which is not only stated in the definition of the section 

 and of the genus, but is even taken for the basis of 

 classification in the primary division of Diatomece non 

 vittatce astomatica, clearly fails in very many species, 

 {pr&morsa, aequalis, mesolepta, Ulna, danica, splendens, 

 armoricanc, sigmoidea, scalaris,} in which these striae are 

 continuous, as in Denticulce. The D. oUonga may be 

 compared with the above-named species. And it is also 

 to be remarked, that though the transverse striae are 

 continuous in these species, as Kiitzing has accurately 

 delineated them, still the characteristic transparent median 

 line remains visible when the object is withdrawn to the 

 remotest extremity of the -microscope, which proves that 

 there must be a longitudinal furrow traversing all the 

 striae ; and to ascertain its depth it would require that 

 the screw regulating the movement of the stage or of the 

 microscope should be micrometric. This slight furrow is 

 also visible in a fragment that accidentally presents the 

 transverse section of such a Synedra. The type of this 

 section is S. Vina, and many other species as well as this 

 (acuta, oxyrhyncus, amphirhynchus, valens, armoricana, 

 sigmoidea, vermicularis,} have the primary surfaces per- 

 fectly linear; but others, again, have the extremities of 

 these surfaces attenuated (debilis), like the greater part 

 of those of the preceding section ; others only rotundate, 

 (premorsa, spectabilis, scalaris ;) in reverse of these 

 many are contracted in the middle, and cuneate and 

 truncate at the extremities, (lanceolata, mesolepta, aequalis, 

 vitrea, danica, splendens, biceps, capitata.) Among the 

 latter we have three, (danica, biceps, capitata,} which, in 

 the important character of capitate extremities of the 

 secondary surfaces, resemble the amphicepliala of the 

 preceding section. And in the greater number of species 

 in this section, as well as in some comprised in the 



26 



