o'mEAKA OX DIATOMACEiE COLLECTED OFF THE ISLAND OF ARR.IX. 109 



described by the late lamented Dr. Greville in the last number of the 

 "Microscopical Journal." Navicula denticulata, however, is distin- 

 guished from that just referred to by the following characters : — It is 

 much shorter and broader, the marginal striae are longer, the central 

 striae are nearer to the median line, and continuous, instead of being in- 

 terrupted towards the central nodule, as in the case of Navicula JEgyp- 

 tiaca. 



Navicula Wrightii. — N". sp., O'M., Fig. 4. Valve broadly elliptical ; 

 length, -0041; breadth, -0024; striae fine, marginal ; there is a broad 

 band at either side of the median line, linear, interrupted towards the 

 central nodule, slightly constricted as it approaches the marginal band 

 of striae, and then expanding towards the apex, which is mammiform. 

 This longitudinal band is destitute of striae. 



On first inspection, this form is liable to be mistaken for N. Hen- 

 nedyi ; but it is distinguished from it, not only by its mammiform 

 apices and the spathulate extremity of the longitudinal median band, 

 but also by the fact that in the present species this band is blank, while 

 in N. Kennedy i it is striate. 



A variety of this species is described in Fig. 4, a, much smaller 

 than the other, and having the sides nearly parallel; length, *0020; 

 breadth, 0014. 



Navicula amphoroides. — N. sp., O'M., Fig. 5. Valve elliptical, nar- 

 row ; length, -0032; breadth, -0014. In this form the central nodule 

 is depressed, and the median line waved ; striae moniliform, in the middle 

 approaching the central nodule, and becoming gradually shorter towards 

 the extremities. 



Pinnularia Arraniensis. — IS", sp., O'M., Fig. 6. Valve broadly ellip- 

 tical; length, -0030; breadth, *0017; striae coarse, distinctly costate, 

 not reaching the median line. 



In some respects this form resembles Navic. Smithii and Navic. <bs- 

 tiva (Donk.) ; but differs from the former by its distinctly costate striae ; 

 and from the latter, by the coarseness of its striae, as also by the fact 

 that it is much broader in proportion to its length than N. eestiva. 



Pinnularia divaricata. — N. sp., O'M., Fig. 7. Broadly elliptical, 

 costate; length, '0058; breadth, *0035 ; the ends slightly produced and 

 rounded ; the central space large, with an outline resembling the ver- 

 tebra of a fish. Through this space there runs a well-marked median 

 line, very fine at the outward extremity, and becoming broader towards 

 the centre, at some little distance from which it terminates in a small 

 bulb. The costae are arranged concentrically with the apex at either 

 end for about one -third the length of the frustule, while those in the 

 intermediate portion spring from the margin of the central nodule ; the 

 central costa runs at right angles with the longitudinal axis, and those 

 at either side radiate towards it more and more as the distance from 

 this line increases ; the costae in the central part of the valve are fur- 

 cate ; in some the furcation appears near the outer margin of the valve ; 

 in others near the central nodule ; some few are bifurcate. 



VOL. v. Q 



