O'Meara — Report on the Irish Diatomacece. 323 



'of little or no significance these peculiarities of growth, which, although 

 subordinate to the general structure of the frustules, should not he 

 overlooked. These differences, as they occur normally, are doubtless 

 assignable to some peculiarity in the structure of the plants which 

 regularly develop them. They therefore demand the careful atten- 

 tion of the students of nature, and, as I think, ought to be marked 

 by a special designation. 



(a). Chlamydicc — Frustules enveloped in a more or less definite frond. 

 Genus I. Mastogloia, "VYm. Smith and Thwaites. 



Mucous frond in such species, as have been observed in situ, papil- 

 late, the frustules imbedded in the top of the papillae ; frustules fur- 

 nished with narrow-marginal silicious plates interposed between tlio 

 valve and the connecting band. 



Klitzing, (Bac. p. 92, T. xxx., fig. 37,) describes a fonn under the 

 name of Navicula meleagris, which evidently belongs to this genus. 

 Thwaites, Ann. Nat. Hist., March, 1848, gives a description of another 

 form belonging to this genus, under the name of Dickiea danseii, but 

 when the characteristic difference in the form of the mucous invest- 

 ment was pointed out by Smith, (B. D., vol. ii., p. 64), he estab- 

 lished the genus Mastogloia to receive a new form discovered by 

 himself, as well as some others that had meanwhile been brought 

 under his notice. The genus therefore may in some measure be 

 attributed to Smith ; the more so because he first seems to have 

 noticed and described one of the most important features in the 

 structure of the frustule. He says, "The frustules of Masto- 

 gloia are notably distinct from those of any other genera of the tiibe 

 having the annulate structure, described under the genus Ehabdonema 

 with the conspicuous canaliculi of a Surirella. In the present case, 

 the canaliculi which take the form of loculi are, however, formed 

 differently from those of Surirella, not being connected with the 

 valve, but with the annulus, which projects as a septum into the body 

 of the frustule." And again, " Normally the annular septum extends 

 only partially across the interior of the frustule, but occasionally the 

 lociili are seen to reach nearly as far as the median line of the valve." 

 ■ — B. D., Vol. ii., p. 63. In reference to this description, Grunow re- 

 marks, " I have been unable to convince myself of the correctness of 

 Smith's supposition, that the costae which according to him form dia- 

 phragms arc attached to the connecting membrane. After numerous 

 observations, I find they are quite analogous to the costae of other 

 Diatoms, and are an inner layer of the silicious plate which in this in- 

 stance separates itself from the outer layer more easily than in other 

 Diatoms."— Verhand. der K. K. Zool. Bot. Gesel., Band x., 1860, 

 p. 674. Hciberg's views on the subject of dispute are thus ex- 

 pressed : " Smith on the contrarv took an erroneous view of the genus 



