MEW OK CRITICAL BRITISH MARINE ALG^. 387 



more or less swollen here and there, much and irregularly hranched, 

 interwoven, forming a network from which very short, few-celled, 

 erect filaments arise, and breaking through the cortical layer of the 

 host-plant terminate in a sporangium ; cells of the decumbent 

 filaments G-18 /x long by B /x in diameter, those of the erect fila- 

 ments about as long as or a little longer than broad, and of about 

 the same diameter as the decumbent filaments ; monospores nearly 

 globular, about 6 /x in diameter, terminating the erect filaments, 

 which are composed of from one to three or four cells. In the 

 cortical layer oi iJasya coccmea, Plymouth, G. Brcbner. 



This minute species bears the same relationship to the other 

 species of AcrocJuctiiDii that Uhodochorton mcmhranaceum Mag. does 

 to the other Rhodochortones. 



10. Peyssonnelia rupestris Crn. Flor. Finist. 148, tab. 19, 

 gen. 129. On old shells dredged from the " Queen's Ground," 

 Plymouth. I detected this pretty little species on some old shells 

 sent to me from Plymouth by Mr. Brebner. The species is dis- 

 tinguished from the other Peyssonnelm by the very thin frond 

 firmly adherent to the substratum, and entirely destitute of rhizoids ; 

 by the almost square cells of the thallus, the comparatively very 

 large tetraspores, and the short paraphyses, which are about as 

 long as the tetraspores, and, except in their greater slenderness, 

 but slightly differentiated from the thallus-filaments. 



11. Cruoriopsis Hauckii, nov. nom. = Cruoriclla armorica 

 Hauck, Meeresahf, 31, non Crouan, Aim. Sc. Nat. 4th ser. xii. t. 22, 

 fig. G. 34-37, nee Crn. FL Finist. 148, t. 19, gen. 128. Fronds 

 forming thin, crust-like, purple-red expansions, closely adherent to 

 the substratum, roundish or irregular in outline, from 1 to 3 mm. 

 in diameter, and from 50 to 100 /x thick ; the younger fronds fre- 

 quently overlapping the older ones ; cells at the base of the erect 

 filaments 10-15 /x in diameter, and about as long as or a little 

 longer than broad, those towards the apices three or four times 

 longer than broad, and only 4 or 5 /x in diameter ; tetraspores 

 immersed in the substance of the frond, 24-30 /x long by 15-20 [x 

 in diameter, irregularly divided, terminal on shortened thallus- 

 filaments. On stones dredged off the west end of the breakwater, 

 Plymouth, G. Brebner. 



As originally described by the brothers Crouan, the genus 

 CruorieUa appears to be very closely related to Fei/ssonnelia, and 

 to differ from it only in the slightly different form of the paraphyses 

 and the fan-shaped disposition of the cell-rows of the basal layer, 

 characters which induced the late Prof. Schmitz to refer the well- 

 known Pei/ssoniielia Dubtji Crn. to this genus. On the other hand, 

 the plant described by Hauck as CruorieUa armorica is evidently 

 not the same as that described by the Crouans under the same 

 name, but is much more nearly related to Cruoriopsis cruciata Duf., 

 as the tetraspores are immersed in the substance of the frond, not 

 produced in superficial nemathecia as in CruorieUa, and the thallus- 

 filaments are only loosely united to one another, while in CruorieUa 

 they are firmly united into a more or less parenchymatous layer. 

 From Cruonopsis cruciata it is distinguished by the much larger 



