\1\NN DIATOMS OF THE ALBATROSS VOYAGES. ZOi 



genus into two, viz: Melosira \.g. Thwaitee and Orthosira Thwaites, rejecting, 

 however, Thwaites's third genus Vulacoseira. Smith defines th< two .1- follow 

 Melosira, "Filaments cylindrical, of numerous frustules, attached 01 free; frustule* 

 spherical or Bubcylindrical, more or less convex at the junction surface* Ortl 

 • • Filaments cylindrical, of numerous frust ules, continuous, attached or free; frusl ules 

 and valves cylindrical; junction surfaces plain, line of junction usuall) 3pin< 

 denticulated." Schmidt, in his Atlas, and a fevi other authors have adopted this 

 division, bul as a genera] rule the distinctions are fell to be too unimportanl and 

 inconstant to warrant the change. Many authors, as Van Heurck, while rejecting 

 Smith's division, have made use of these minor differences within the genus for 

 subgeneric classification. The untenable proposal of II. !.. Smith i" unite this genu.' 

 with Podosira and Hyalodiscus will be < I i-< u-~><' I under the name Podosira in this 

 reporl . 

 Melosira P coronaria Mann. sp. nov. I'i vn. LI, ftgi res I. _'. 



Valves consisting of two portions: First, a broad border curving downward, its 

 outer half closely punctate with Bhining granules and its inner half marked with 

 line radiating Inn - closely set, the line of division between the punctate and striate 

 halves being a wavy one; second, a central area raised above the border by a 

 cylindrical hoop, seen in the zonal view, thi.- central area being flat and perfectly 

 hyaline. In 1 he zonal view of the valve is seen, rising above the curved border, the 

 before-mentioned hoop or band, the lower two-thirds of which i- cylindrical and 

 terminal" s in a row of small l>ni stoul tubular processes equidistant and ha\ ing Mum 

 ends, extending obliquely outward and upward, their bases surrounded bj a fringi 

 of irregular spines. Between each pair of these processes are one to three smaller 

 ones. The upper one-third of the hoop or band, that is, between the ring of processi 

 and the llai hyaline top, is a flaring ornamented rim. The cylindrical lower two- 

 thirds of the hoop or band is covered with minute beading, arranged in regular 

 3-line older: the upper flaring one-third of the hoop or hand is covered with fine 

 vertical lino forming a leaf-like sculpl ure by each of four or five bending toget her at 

 the n»p. 



Diameter of valve, <>.s:; mm.; height of valve < zonal view), 0.25 mm. 



This diatom i- certainly generically the same as Porodiscus (Pyrgodiscus ? calcy- 

 flos Temp. A: I'-run." which is the same as Porodiscus interruptus Gr. A Si..'- this in 

 turn being the same as Porodiscus hirsutus Gr. A St., c Grove and Sturt's specimens 

 being the inner area of Tempere A Brun's. It is even closer to what Schmidl 

 call- /'. calcyfios Temp. & Br.d which is misnamed, as his figures In. 11 of the same 

 plate, called /'. hirsutus Gr. A St. are Tempere & Brun's type. If, therefore, my 

 specimens are to follow 1 he generic assignment of 1 hex- \ ery similar forms, they would 

 hear the name Porodiscus corona/ins Mann. But 1 am convinced that this generic 

 name is utterly inapplicable to all these form.-. They have nothing in common with 

 Greville's genus except the central pore-like area.< As even this disappears in the 

 figures of /'. calcyfios,) and in my own specimens, this character, totall) inadequate 

 in itself, is eliminated and there does«no1 remain any semblance to the Porodiscus 

 type. Neither can they be included in Pyrgodiscus Kiit.r/ Tempered Brun suggest 

 this idea by bracketing Pyrgodiscus with their name. But Kitton!s genus, with it 

 centra] tower-like elevation whence the name, bearing four enormous spines with 



"Mem. Soc. Phys. ei Bist. Nat. Geneva 30": 50. pi. ,./. 11. 11a. 1889 

 &Journ. Quek. Micr. Club, 1 1. 3: 67. pi. 5. /'. 8. 188 

 1 < )p. eii. I 1:;. pi. 1 ;. /'. :>',. 

 'i Schmidt, Atlas pi. 158. f. >. 9. L890 



'('\. Porodiscus Grev. Trans. Micr. Soc. Lond. n. >. 11:63. pi. ,. f. 1 >. 1863. 

 ' Schmidt. Atlas t >1 . 158. f. 9. L890. 

 fJourn. Quek. Micr. Club 11.2: 17:;. pi. /.;. f. IS a c. 188 • 



