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1 



MANX DIATOMS OF THE AL13ATKOSS VOYAGES, 237 



gonii^ iiiLo two, viz: M(.'lot>ira (Ag.) Thwaitos and Orthosira Tliwaites, rojecting, 

 liowt^ver, Tliwaites'K third genus Aulacoseira. Smith defines Ihc^ two as follow.^: 

 M(du8ira, ''Filaments cylimhical, uf numeruuri frustules, attached or frcH'; frustides 

 ppherieal or sul)eylindrieal, more or h'lsw convex at the junction surfaces;'' Orthosira, 

 ^ "Filaments cylindrical^ of numerous frut?tules, contiimous, attached or free; frustules 

 and calves cylindrical; jundion surfaces plain^ lino of junction usually si)iiious or 

 denticula((Kl. " Schmidt, in his Atlas, and a few other authors have adopted this 

 division, but as a general rule the distinctions are felt to be too unimportant and 

 inconstant to wariant the changes Many authors, as Van TTeurck, Avhilc rejecting 

 Smilirs division, hav(^ made use of thesc^ minor differeiues witliin tlu^ g(^nus for 

 subgeneric cla^ssilication. The untenable proj)osal ol II. li. Snuth to iniite this geiuis 

 with Podosira and Hvalodiscus will be discussed under the name Pudosira in this 



rf^port. 



Melosira ? coronaria Mann, sp. nov, Plate LI, figlkks 1, 2. 



Valves c(msisting of two portions: First, a broad border curving dt>wnward, its 

 outer half closely punctate with shining granules and its inner half markf^d with 

 fine radiating lines closely set, the line of division between the j)nnctat(^ and striate 

 halves being a wavy one; second, a central an^a raised above the border l>y a 

 cylindrical hoop, seen in the zonal view, this central ar'^a l>eing flat and perfectly 

 hyaline. In the zonal view (tf tht* valve is seen, rising above lln^ ctnved border, the 

 befori^-mentioni'd 1uju]> uv band, the lower two-tlnrds of which is cylindrical and 

 terminates in a row of small but sttnit tubular processes (Kiuidistant and ha^vingbbinl 

 ends, extending oblirpiely outward and upwanl. their bases surround<'d by a fring<' 

 of irregidar spines. Retw(»en each jtair of thes(; processes are one to tlu'ee smalh^r 

 onc^s. The uppcT one-third of the hoop cr ban<l. that is, between the ring of processes 

 and file flat hyalin(^ top, is a flaring ornamented rim. Th(^ cylindri<'al Inwer two- 

 tliirds of the lioop or band is cov(T(kI with ndnutc beading, arranged in regular 

 3-line (jrder; the uj)per flaring one-third uf the hoop or band is covered with fint^ 

 verlical lines fornung a leal' like sculpture by each of four or five bending together at 



tin* top. 



Diameter of valve, 0.S3 nun.; height of valve (zonal view), 0.25 jum. 



Tins <liatoni i^ certainly generically the same as Porofli^cus (PynjodLscus ?) culcy- 

 flos Tenij). & Pirun/' which is tlw sann* as Forodii^vus inlemfptitf; Ca\ & St,.^ this in 

 turn being the sann? 'as Porodiscus hirsifftts (Jr. & St..(' Gn>ve and Sturt^s specimens 

 being the inn(*r an^a of Tempen* & Prun's. It is even closer to what SchTnidt 

 calls F. calnjfos Temj). k V^yA wliich is misnam<\l, a.s his figures 10, 1 I of the same 

 plate, called F, hlrsutus Or. A: >St. are Tempere & P>run's type. If, then>for(% my 

 specimens are to folloM' the generic assignnu^nl of these very similar forms, they wouhl 

 bear the name Forodiscus coronarius Mann. Put I am convinced that this generic 

 name is utterly inapplicable to all the^e forms. Tlu^y have n(4hing in conuu'jn with 

 Greville's genus except the cenual jx^re-like area.*^ As even this disappears in the 

 figures of F'. calcfjjlos,/ ami in my own spe(imens, this character, totally inadc^quate 

 in itself, is eliminate<l and th<T(^ d(t(^s not remain any semblance to the Porodiscus 

 typ(\ XeitluM* can they Ix^ included in Pyrgodiscus Kiit.i/ Tenii)ere & P>rnn suggest 

 this idea liv Ijrackt^tin^ Pvr*j:ot|iscus wilh llieir nanu'. Pvit Kilton's genus, willi its 

 central tower-like elevation (whenc(^ the nann\5 })earing four enormous spines wilh 



a:Meni. So<'. Phys. cL Hist. Xat. Geneva 30'': 50. pi. 4^J\ //, ^hi. ISSf). 



?> Journ. Quek. :Micr. Tlub, IP 3: (17. pL .7. f. S. 1887. 



cOp. cit. U.'^. pL 14. f- '>4. 



d Schmidt, Atlas pL ir>S.f. A', .9. 1890. 



eCi. Porodiscus Grev. Trans. Micr. Soc. Pond. n. s. 11: 11.'^. pi. 4.f. 1 -7. 1803. 



/Schmidt, Atlas p?. ir^H.f'.U, 1890. 



£7jom-n. Qu<'k. Micr. rbil) IP 2: 173. pL F'^.f. Fl a-e. issr>. 



