78 o'mEAUA; on DIATOMACEiE. 



the valves are larger than those of S. fastuosa, their breadth 

 is considerably less. 



When Mr. Kitton suggested that Pinnularia comtricta may- 

 be "possibly a form of Navicula truncata, a very variable 

 species both in size and costce," I presume he referred to a 

 species so named in Dr. Donkin's interesting paper published 

 in the'Mic. Journal/ Jan., 1861. The side view of Dr. 

 Donkin^s form is not described^ and from a careful com- 

 parison of my form with his figure I considered they were 

 distinct. In any case the specific name of Truncata for that 

 form must be dropped, because Kiitzing, in his ' Bacillarien 

 oder Diatomeen,' taf. iii, fig. 34, and taf. v, fig. 4, has figured 

 and described a form with this specific name which bears no 

 resemblance to Pinnularia constricta. 



But further, some of Mr. Kitton's conjectures seem to me 

 untenable, except on principles which would have the effect 

 of involving the classification of the Diatoms in utter con- 

 fusion ; for if Navicula denticulata is to be confounded with 

 N. imndura — N. amplioroides with AmjjJwra salina (in which 

 case I must assure Mr. Kitton that the suggestion so un- 

 graciously offered in the " query, is not the nodule a small 

 grain of quartz ?" is the baseless figment of his fancy) — Rapho- 

 neis Archeri with Cocconeis costata or C. clavigera — Eupo- 

 discus excentricus with Coscinodiscus minor — the hope of dis- 

 tinguishing species with any reasonable certainty must be 

 abandoned in despair. 



In the case of Raphoneis Archeri there is nothing to sustain 

 Mr. Kitton's conjecture that the puncta have been abraded. 

 Since the paper describing it was published, the same form 

 has been fovmd by me in considerable abundance on sea- 

 weeds from the Falkland Islands and from Kerguelen's Land. 

 In the structure of Eupodiscus excentricus there is not even a 

 remote resemblance to that of Coscinodiscus minor. Had 

 Mr. Kitton identified it Avith Coscinodiscus excentricus, he 

 would have had some reason to support his view, for in this 

 form the sculpture is similar to that of Coscinodiscus excen- 

 tricus, a fact which suggested the name. This form frequently 

 occurred in the dredgings, and invariably exhibited the pecu- 

 liarities noticed — a smooth submarginal border, and distinct 

 processes on the secondary surface. Even suppose it be con- 

 ceded that the former is, as Mr. Kitton suggests, " an abnormal 

 marginal development," he has not accounted for the latter, 

 namely, the processes which seem to remove the form from 

 tlie genus Coscinodiscus, as defined by the latest published 

 authorities on the subject. 



