DESCRIPTION OF GENERA AND SPECIES. 



TRIBE I.— RAPHIDIE^. 

 Amphora, Ehrenb. 



The essential characters of the frustules of this genus are so difficult and complicated 

 as to be but little understood. So much is this the case that Professor Arnott severely 

 writes l that Dr Gregory having, in his pamphlet on the Diatoms of the Clyde, failed to 

 indicate their distinguishing features, has thereby deprived his work of its claims to be 

 considered scientific. These observations adequately prove the magnitude of the dif- 

 ficulties that exist, and indulgence may be claimed for any errors that occur in the 

 treatment of so obscure and intricate a genus. 



The general form of an Amphoran frustule may be taken to resemble that of a grain 

 of coffee, but Dr Gregory's conception that the so-called frustule should be regarded as 

 two perfect frustules that have become united apart from any process of conjugation 

 cannot be entertained. If some species occur as very delicate cymbelloid forms, such as 

 Amphora cqffcceformis, Kg., this is attributable to the character of the connecting zone, 

 which is extremely slender, and which may be destroyed by the slightest possible action of 

 acids, even when diluted, or by fire. 



Amphora speciosa, n. sp. (Plate XXVII. fig. 1.) 



Elliptica sublinearis ; apicibus rotundatis ; valva introrsum infiata ; striis punctulatis 

 subradiantibus. Ad portum Thaiti. 



This species would perhaps be identical with Amphora oblonga, Greg., 2 were it not for 

 the profile of the frustule, which is described by Gregory as " elliptic, rather broad," with 

 " ends obtusely acuminate." The present form, however, is narrow, its margins are almost 

 linear, and its extremities are rounded less sharply. The striation also differs in the two 

 cases, being subradiate and evidently moniliform in Amphora speciosa, while in Amphora 

 oblonga it is continuous. This new species, which is figured in its zonal aspects, was 

 obtained at the port of Tahiti. 



Amphora meneghiniana, n. sp. (Plate XXVII. fig. 16.) 



Sublineariter elongata ; apicibus rotundato-truncatis ; medio late subinflata ; striis 

 transversis conspicuis subradiantibus. Ad portum Thaiti. 



This magnificent new species was also first obtained at the port of Tahiti. It is of an 



1 Quart. Journ. Microsc. Sci., vol. vi. p. 184, 1858. 2 Diatoms of the Clyde, p. 43, pi. v. fig. 78. 



(bot. chall. exp. — part iv. — 1886.) D 3 



