OF THE MELOSIRE^. 



815 



H. suhtilis (Bai.). — " Disc marked like 

 the engine -turned back of a watcli, with 

 lines of exceeding delicacy, only visible 

 by the highest magnifiers and careful 

 illumination ; umbilical portion more 

 coarsely granulated and in size little less 



than one-third of the diameter of the disc," 

 B. /. c. pi. 1. f. 12. Halifax, Nova Scotia. 

 '^ H. Icevis differs by having a wider mar- 

 gin and much coarser markings. This 

 species forms an admirable test-object," 

 B. (v. 60.) 



Genus LYSICYCLIA (Ehr.). — The characters of this genus are unknown 

 to us. From Ehrenberg's figures it appears closely related to Hyalodiscus, 

 the disc having a central, circular umbilicus, and a broad border separable at 

 the suture, as in that genus. 



LYSICYCLIA Vogelii, ERBA. 1856, p. 333, f. 29. Central Africa, (viii. 39.) 



Genus PODODISCUS (Kiitz.).— Frustules as in Podosira, but affixed by a 

 lateral stipes. Marine. We think that the lateral position of its stipes is 

 scarcely sufficient to separate Pododiscus from Podosira. 



pi. 16. f. 28. On Enteromorpha ramidosa, 

 Jamaica. Diam. 1-840". (xni. 28.) 



Pododiscus Jamaicensis (Kiitz.). — 

 Frustules simple, concatenate, smooth ; 

 stipes elongated, delicate. KSA. p. 26, 



Genus PODOSIRA (Ehr.). — Frustules united into short filaments, having* 

 a distinct central stipes ; interstitial portion obsolete ; valve convex. Marine. 



In Podosira the lateral valves are vaulted, and the central portion is at 

 first a mere connecting ridge between them. This ridge, however, becomes 

 gradually broader, and then double; afterwards an intermediate growth 

 separates the halves of the frustule, which meanwhile do not increase in size ; 

 and at last, when the intermediate space equals the diameter of the original 

 frustule, two new frustules are formed by the addition of a hemisphere on 

 the inside of each of the separated portions. The outer silicious covering* 

 stiU remaining, the frustules are connected in pairs, and appear hke two 

 globules within a joint. The valves usually have a central, coloured umbi- 

 licus — an appearance which Professor Smith attributes, in our opinion errone- 

 ously, to an absence of silex at that point. 



Podosira Montagnei (Kiitz.). — Frus- 

 tules subspherical, dotted ; connecting 

 sheath with parallel annidar series of 

 minute stride. SBD. ii. pi. 49. f. 326. 

 =P. Adriatica, Me. on Diat. ; 3Ielosira 

 qlohifera, Ra ANH. xii. Britain, France, 

 &c. ' (v. 61.) 



V.Hormoides (Kiitz.). — Frustules oval, 

 united into short moniliform filaments ; 

 connecting sheath obscm-ely punctate ; 

 lateral view with umbilicus but no rays. 

 SBD. pi. 49. f. 327. = P. mimmidoidesi'E,. 

 (ii. 45.) Atlantic, Britam, &c. Di- 

 stinguished from the preceding species 

 by its more depressed valves. 



P. macidcda (S.). — Disc with a large 

 central umbilicus, which is bordered by 

 an irregular, fracture-like suture, from 

 which radiate outwards several shadow- 

 like bands ; surface punctated. SBD. ii. 

 p. 54, pi. 49. f. 328. Common in deep 

 water, guano, &c. Britain. It may be 

 identical with Crasjyedodiscus Stella, E. 

 P. conqjressa, West. (viii. 34.) 

 P. Icevis (Greg.). — Frustides trans- 

 parent, glassy, with very delicate oblique 

 striae and scattered puncta; connecting 

 zone distinctly striated ; disc without a 

 distinct umbilicus. Grev MJ. vii. p. 85, 

 pi. 6. f. 15-17. Scotland. 



Genus MELOSIRA (Ag.). — Frustules cylindrical, discoid, or globose, con- 

 nected into cyhndrical conferva-like filaments, one or two lines passing 

 round each frustule near the centre. = Gallionella, Ehi*. Maritime and aquatic. 

 This genus is easily distinguished from the other genera of the Diatomaceae 

 except Pododiscus, with which the species in its first section closely correspond 

 in character. The filaments are remarkable for their conferva-like appear- 

 ance, but may be known by their brown colour and very fragile nature. The 



