9 
O’Mrara—Report on the Irish Diatomacee. 323 
of little or no significance these peculiarities of growth, which, although 
subordinate to the general structure of the frustules, should not be 
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). Chlamydia—Frustules enveloped in a more or less definite frond. 
Genus I. Masroetora, Wm. Smith and Thwaites. 
Mucous frond in such species, as have been observed 7m situ, papil- 
late, the frustules imbedded in the top of the papille; frustules fur- 
nished with narrow-marginal silicious plates interposed between the 
valve and the connecting band. 
Kiitzing, (Bac. p. 92, T. xxx., fig. 37,) describes a form 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 danseu, but 
when the characteristic difference in the form of the mucous invest- 
ment was pointed out by Smith, (B. D., vol. u1., 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- 
gioia are notably distinct from those of any other genera of the tribe 
having the annulate structure, described under the genus Rhabdonema 
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 
loculi are scen to reach nearly as far as the median line of the valve.” 
—B. D., Vol. u., 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 costz which according to him form dia- 
phragms are attached to the connecting membrane. After numerous 
observations, I find they are quite analogous to the coste 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- 5/4. Heiberg’s views on the subject of dispute are thus ex- 
pressed: ‘‘ Smith on the contrary took an erroneous view of the genus 
