MELOSIRA. 



[ 498 ] 



MEMBRANES. 



three, enclosed in two sheath-like, hairy, 

 unjointed organs (labial palpi), resembling 

 otherwise those of Pulex, and arising from 

 the sides of a triangular labium. Legs 

 robust ; tarsi with two stout serrated claws, 

 each having at its base a blunt process ; 

 accompanying the claw is an elegant feathery 

 tarsal brush ; and on the under side of the 

 last tarsal joint is a bilobed pectinate organ. 



BIBL. Lyonnet, Anat. et les metamor. ; 

 Gurlt, Magaz.f. d. gesam. Thier. 1843, ix. ; 

 Westwood, Introd. ; Curtis, Er. Entom. 142 ; 

 Pufour, Ann. Sc. Nat. 1845, iii. ; Leuckart, 

 Fortpflanz. der Pupiparen. 



MELOSI'RA, Ag. (Gallionella,~Eh?). 

 A genus of Diatomacese. 



Char. Frustules cylindrical, discoidal or 

 subspherical, united into jointed filaments. 



Hoops often very broad, to adapt them- 

 selves to the breadth of the new irustules. 

 In some species a narrow projecting ridge 

 or keel encircles the valves near their ends. 

 Valves covered with dots, which are mostly 

 very minute and invisible under ordinary 

 illumination ; in the side view they some- 

 times have a radiate arrangement. In some 

 species the margins of the ends of the frus- 

 tules (side view) have coarse and distinct 

 radiating striae. 



This genus has been subdivided by 

 Ehrenberg and Kiitzing into : Lysigonimn, 

 in which the keel is present ; and Gallionella 

 (proper), in which this is absent. Again, by 

 Thwaites into : Aulacosira, in which the 

 frustules are cylindrical, surrounded trans- 

 versely by two furrows, with rounded (con- 

 vex) ends, but no line for division ; Orthosira, 

 in which the frustules are exactly cylindrical 

 (with flat ends), exhibiting the transverse 

 line of division, and with spherical or sub- 

 spherical internal cavities; and Melosira 

 (proper), in which the frustules are convex 

 at the ends, and have the central line of 

 division. 



Numerous British species. 



* Marine. 



M. nummuloides, Kg. (PI. 17. fig. 5 a; 

 b, a frustule more magnified). Prepared 

 frustules colourless, distinct keel present ; 

 valves without markings under ordinary I 

 illumination; breadth 1-1500 to 1-1200". 



This common species forms long, slightly 

 curved chains, and, on account of the great 

 breadth of the frustules, shows well the 

 various stages of subdivision. The filaments 

 are sometimes stipitate. 



M. Borrerij Grev. Prepared frustules 

 dark brown, ends rounded, entire surface 



punctate (ordin. ilium.), no striae nor keel j 

 breadth 1-850 to 1-500". 



M. Dickiei (Orthosira Dickiei, Thw.) 

 (PI. 17. fig. 15: 0, front view; 6, side view). 

 Filaments short, frustules nearly colourless, 

 ends flat, no striae nor keel (ord. ilium.), 

 valves thickened so as to render the cavity 

 of the fruetules rounded ; breadth 1-1500 to 

 1-1200". 



The remarkable sporangia formed in this 

 species (PI. 10. fig. 9) are noticed under 

 DIATOMACE^;, p. 249. 



** freshwater. 



M. (Orthosira') variant (PI. 17. fig. 6, 

 front view; a, side view). Frustules colour- 

 less, ends slightly convex and striated at the 

 margin (ord. ilium.), keel absent; breadth 

 1-1500 to 1-1200". The end view of the 

 frustules resembles that of Cyclotella. 



Formation of sporangia shown in PI. 10. 

 fig. 8 a ; 6, sporangial frustule. 



M. arenaria. Ends of frustules flat and 

 striated at the margin (ord. ilium.), the striae 

 appearing also in the front view ; keel 

 absent ; frustules broader than long ; breadth 

 1-660 to 1-260". 



M. crenulata, Kg. (Aulacosira crenulata, 

 Thw. ; M. orichalcea, Ralfs) (PI. 10. fig. 7 a, 

 forming sporangia; 6, c, sporangial frus- 

 tules). Differs from the last in its less 

 diameter, and the frustules being two or 

 three times as long as broad; breadth 

 1-1400". 



BIBL. Kiitz. Bacill 52, Sp. Alg. 27; 

 Ralfs, Ann. N. H. 1843, xii. 346 ; Thwaites, 

 ibid. 1848, i. 168 ; Smith, Br. Diat. ii. 54 ; 

 Rabenh. Alg. ii. 37 ; O'Meara, Q. Mic. Jn. 

 ix. 150. 



MELOXAN'THUS, Buckt. A genus of 

 Aphidae.. M. salicis. Black, legs orange, 

 antennae 7-jointed; on the willow. (Buckton, 

 Aphid., Ray Soc. ii. 21.) 



MEMBRANES, UNDULATING. These 

 are said to be simple membranous bands, 

 one margin only of which is attached, the 

 other being free and exhibiting an undu- 

 latory motion. They are allied to and 

 answer the same purpose as cilia. They 

 are described as occurring upon the sper- 

 matozoa of salamanders and tritons; as 

 forming longitudinal processes in the water- 

 vessels of some Anellida, as the Turbellaria ; 

 also as existing in some Infusoria, as Tricho- 

 dina, and some Rotatoria. Some authors 

 have regarded them as consisting of rows of 

 cilia or, a .spiral fibre, and not membranes. 

 They are most easily examined in the sper- 

 matozoa of the triton, in which we believe 



