RHOIKONEIS. 



[ 059 ] 



RICCIA. 



a central nodule in tlie curved side. R. cur- 

 vata (PI. 52. fig. 19). 



BIBL. Rabenht. Alg. i. 112. 



RHOIKONE'IS, Grun. A subgenus of 

 Achnanthidium, comprising two species, 

 found in the North Pacific. 



BIBL. Rabenht. Alg. i. 109. 



RHOPALOMY'CES,Corda. Agenus of 

 Mucedines (Hyphomycetous Fungi), nearly 

 allied to ASPERGILLUS, but having the 



Fig. 618. 



3 



Fig. 619. 



Khopalomyces nigra. 

 Fig. 618. Tufts on wood. Nat. size. 

 Fig. 619. Fertile filaments. Magnified 200 diameters. 



spores single (fig. 619), and not in monili- 

 form series. The single spores are borne 

 on minute spines (fig. 619, left-hand head). 

 Thev are mildews growing over decayed 

 wood, matting, dung, &c. Two new British 

 species are described by Berkeley and 

 Broome, found growing together. 



BIBL. Berk, and Broome, Ann. N. H. 2. 

 vii. 96, pi. 5. 



RHOPALOSPPHUM, Koch. A genus 

 of Aphidse. Six species, on the currant and 

 gooseberry, Sonchtis, Alisma, Ligustrum, 

 and Herberts. (Buckton, Aphidce } Ray Soc. 

 ii. 9.) 



RHUBARB. Garden rhubarb (Rheum 

 undulatum, and other species) affords, in the 

 large edible petioles, excellent specimens of 

 SpiRAL-fibrous STRUCTURES, spiral, an- 

 nular, and reticulate vessels and ducts : these 

 are readily isolated by the help of a needle 

 from a fragment of cooked rhubarb placed 

 in water on a slide, and are well seen by 

 polarized light. The petioles and leaves 

 likewise contain bundles of acicular RA- 

 PHIDES. The roots also contain 

 receptacles for a characteristic secretion. 



RHYNCHLE'TA, Zenker. A genus of 

 Acinetina. Body ovate, free or attached, 

 with a long anterior suctorial tentacle. R. 

 cyclopum, freshwater, on Cyclops. (Kent, 

 Inf. 806,) 



RHYNCHOL'OPHUS, Duges, = Enj- 

 thrcws, Latrreille (not Duges). A genus _ of 

 Arachnida, of the order Acarina, and family 

 Trombidina. 



Char. Palpi large, free ; labium penicil- 

 late ; mandibles ensiform, very long ; body 

 entire; coxas very remote, legs palp-like, i. e. 

 dilated at the end, posterior very long. 



Species numerous ; found in woods, under 

 leaves, and in mosses. 



R. cwereus (PL 6. fig. 40 : a, labium with 

 palp; b, tarsus; c, plume of labium more 

 magnified ; d } mandible). 



BIBL. Duges, Ann. So. Nat. 2. i. 30; 

 Gervais, Walckenaer's Arachnid, iii. 175 ; 

 Koch, Deutschl. Crust. ; Murray, Econ. Enl. 

 124. 



RHYNCHONE'MA, Ktz. A genus of 

 ZYGNEMACE^E (which see). 



BIBL ; Rabenht. Alg. iii. 229. 



RHYNCHOP'AGON, Werneck (Rota- 

 toii&)=Diglena with a bilobed rostrum! 

 Two species. (Werneck. Ber. Berl. Ak. 

 1841, 377.) 



RHYNCHOP'ORA, = Lepralia pt. R. 



"^^STOHOPBION. See PULEX. 



RHYTIS'MA, Fries. A genus of Phaci- 

 diacei (Asconiycetous Fungi), growing upon 

 the leaves of trees and shrubs, forming dark 

 patches or spots on the surface, breaking 

 through the epidermis with little scales or 

 irregular fissures. R. acerinum is exceed- 

 ingly common, forming large black spots on 

 the leaves of the sycamore and maple ; the 

 thecasporous fruit is perfected (on the dead 

 fallen leaves) in spring ; MELASMIA acei'ina, 

 which occurs in autumn, appears to be a 

 preparatory form of this plant. R. salici- 

 num is common on willow-leaves. 



BIBL. Berk. Br. Fl. ii. pt. 2. 290 ; Grev. 

 Crypt. Fl. pi. 118; Fries, Sum. Veg. 370; 

 Tulasne, Compt. Rendus, 1852 (Ann. N. H. 

 2. viii. 118) ; Cornu, Compt. Rend. 1878, 

 Grevillea, vii. 100. 



RICASO'LIA. A genus of Phyllodei 

 (Lichenaceous Lichens). 



Char. Thallus lobate or laciniate, affixed 

 by fasciculate rhizinse ; gonidia small, yellow- 

 green ; spores 1-3-septate. (Leighton, Brit. 

 Lich. Flora, 112.) 



RICCIA, L. A genus of Riccieee (Hepa- 

 ticae), consisting of minute green thalloid 

 productions growing upon damp ground or 

 floating on water, distinguished from the 

 allied forms by the capsules being immersed 

 in the substance of the frond, destitute of 

 perichsete and perigone, while the archegone 

 2u2 



