o'mEAKAj on DIATOMACEiE. '}n 



added to my original descriptions of the forms such further 

 particulars as I considered necessary to convey a clear con- 

 ception of the difference between them so obvious to the 

 observer. If these forms be referred to Cocconeis scutellum, 

 they differ from any I have seen in nature, or in the figures 

 of such authors as have come under my notice, and seem 

 entitled to be regarded as undescribed and distinct varieties. 



On this subject T may remark further that Mr. Kittoii 

 appears to confound what I call the border in Raphoneis 

 Jonesii with the cinguluni or hoop which unites tlie two 

 valves of the frustule ; the latter is separable, as he observes, 

 but the former, as an essential portion of the valve, is not 

 altogether an insignificant character of the structure. 



Before Mr. Kitten's remarks came under my notice, the 

 valuable German publication ' Hedwigia ' had made me 

 aAvare that the specific name of gracilis had been previously 

 applied to a form of Surriella, and I had determined on the 

 first occasion that offered to correct my mistake, and give the 

 name Gracillima instead of Gracilis. GrunoAv's figure was 

 familiar to me, and I know not how the name escaped my 

 notice when examining his list, as well as others, to ascertain 

 whether the name I had selected had been anticipated. Mr. 

 Kitten's remarks on Surirella are at variance Avith the views 

 of the highest published authorities on the subject; Dr. 

 Gregory and Dr. Greville, as he frankly acknowledges, differ 

 from him. Pritchard and Grunow in their classification of 

 the genus Surirella make use of those differences in the out- 

 line of the valve and the structure of the costee, Avhich Mr. 

 Kitton considers of little value. Surirella lata and >S'. fastuosa 

 are regarded by these authors, as well as by Smyth, as dis- 

 tinct species. Both the species I have described occur 

 frequently in the Arran dredgings ; the forms belonging to 

 them respectively differ little in outline, and invariably 

 exhibit the peculiarities in the shape and arrangement of the 

 costae which I have noticed in my descriptions. Supported 

 by the example of these authors, so illustrious in this depart- 

 ment of science, I considered myself — and still consider my- 

 self — ^justifiable in giving distinct names to these forms of 

 Surirella. 



In addition to the characters already referred to, I avail 

 myself of the present ojDportunity to notice a peculiarity in 

 the general structure of these forms, which strengthens my 

 reasons for separating them from S. fastuosa. On the side 

 view the valves in these species are flat, whereas in S. fastuosa 

 the centre is deeply depressed, and in the front view, although 



