KErOItT ON THE DIATOMACEiE. 23 



Stauroneis, Ehrenb., Kg. 



Althougli some authors, impelled by a desire of reducing the number of generic 

 distinctions among Diatoms, have united into a single genus not only the Pinnularice and 

 Naviculm but also the Stauroneides and Stauropterm of Ehrenberg, such a course cannot be 

 regarded otherwise than as prejudicial to science. It is to be remarked, however, that the 

 genera Stauroneis and Stauroptera, which do not contain a large number of species, may 

 be amalgamated, so that, following the example of W. Smith, Pritchard, and others, any 

 free navicular frustule with a middle line, terminal nodules, and a central stauros or 

 transversely enlarged nodule, may be called a Stauroneis. 



Stauroneis pacifica, n. sp. (Plate XX. fig. 9.) 



Lanceolato-oblonga ; apicibus obtusis ; nodulo centrali in aream linearem ad marginem 

 attingente ; striis moniliformibus tenuissimis radiantibus, lineam mediam non attingentibus. 

 In oceano Pacifico. 



This frustule possesses a navicular lanceolate form, and is provided with obtuse pro- 

 longed extremities. The stauros extends to both margins. The striae are very delicate 

 granular, radiating and approximately parallel, they are obliquely disposed, and terminate 

 before reaching the median line. 



The species is named after the ocean in which it was first observed. 



Stauroneis thaitiana, n. sp. (Plate XX. fig. 16.) 



Parva, elliptico-lanceolata ; apicibus cuneato-rotundatis ; area transversa lineari brevi ; 

 striis ten uissimis transversis, parallelis. Ad portum Thaiti. 



This small and elegant form from the rich collection obtained at the port of Tahiti 

 possesses an elliptico-lanceolate outline, and is provided with roundly cuneate extremities. 

 The central nodule expands transversely as a narrow linear area which stops before 

 reaching the margin. The striae are very fine, tranverse and parallel. The raphe is 

 enclosed in a smooth narrow linear area. 



Stauroneis salina, W. Sm., var. c, nov. (Plate XX. fig. 13.) 



Probably this frustule must be regarded as a mere variety of the Stauroneis salina of 

 W. Smith. 1 The following points of distinction between the typical species and the variety 

 may however be noted: — (1.) The extremities of the latter are considerably more acute 

 than those of the former; and (2.) the stria?, although erroneously represented coarser in 

 the present species, are approximately of the same degree of fineness in both. 



1 Op. cit. vol. i. p. 60, pL xix. fig. 188. 



