108 NATURAL HISTORY SOCIETY OP DUBLIN. 



cells or granules ; the rays are distinctly marked towards the margin, 

 but somewhat confused towards the centre; puncta or granules larger 

 towards the centre than at the margin." In the other form the rays are 

 distinctly marked throughout the entire length, some of them reaching 

 the centre, others terminating at some distance from it, and others ex- 

 tending but a short distance from the margin. The granules forming 

 the rays are considerably smaller than those of the other species referred 

 to, and the central ones are scarcely larger than those at the margin. 



For these reasons, I consider the two forms should be regarded as 

 distinct species, and suggest that from henceforth the name Coscinodis- 

 cus Gregorianus be given to the form found by Dr. Gregory in the Glen- 

 shira Sand. 



I now proceed to mention a fact deserving of special attention, 

 namely this, that Tessella interrupta, Eupluria pulchella, and forms be- 

 longing to the genus Hyalodiscus and Omphalopelta have been met 

 with in this gathering. These species have been discovered in distant 

 parts of the world, but, so far as I can learn, have not hitherto found a 

 place in the list of British Diatoms. 



But the number of forms which, so far as I can ascertain from the 

 sources of information available to me, have not been hitherto de- 

 scribed, constitutes the most interesting feature of this valuable collec- 

 tion. Some of those I shall hold over for further examination, and now 

 submit for your consideration a few of these new forms, with their de- 

 scriptive characters. 



Navicula Eihernica. — !N". sp., O'M., Pig. 1. Broadly elliptical ; 

 length, -0041; breadth, -0024; striae very fine, confined to a narrow 

 marginal band ; parallel to the median line there is a broad band, with- 

 out striae, linear, interrupted at the central nodule, constricted towards 

 the ends, and rounded ; the central portion of the valve granulated. 



This pretty form is closely allied to Navicula indica (Grev.), but has 

 not the mammiform apices, nor the lyrate blank spaces of that beauti- 

 ful species. 



Navicula pellucida. — N. sp., O'M., Fig. 2. Length -0036; breadth, 

 •0013, constricted ; striae very fine, confined to a very narrow marginal 

 band ; short towards the ends and the central constriction ; the inner 

 part of the valve smooth, pellucid at either side of the median line, di- 

 vided into two compartments by a longitudinal curved line. 



The front view constricted, marked at the centre and ends by bead- 

 like nodules. 



Navicula denticulata N. sp., O'M., Fig. 3. Length of valve, '0034 ; 



breadth, -0013; deeply constricted ; striae costate rather than monili- 

 form, marginal, with a narrow striate, longitudinal band close to the 

 median line, the interspaces blank. 



Probably this form belongs to the Pinnulariae ; but although the 

 reasons assigned for merging the latter family in the Navicular seem 

 scarcely satisfactory, I feel disposed to fall in with the tendency in this 

 direction when the form presents the general characteristics of the Na- 

 vicular. This species bears a striking resemblance to Navicula Egyptiaca, 



