ZYGODON. 237 



Although this is usually a markedly distinct plant, yet intermediate forms are 

 certainly to be found ; and this fact, together with the existence of the var. rupestris 

 above, must be held sufficient warrant for making the present a sub-species of Z. 

 viridissimus, and not allowing it the full specific rank. 



Clavate, jointed gemmse are generally found on the leaves and radicles of this 

 plant, as they are also, but less constantly, on Z. viridissimus. 



4. Zygodon conoideus Hook. & Tayl. (Bryum conoideum 

 Dicks.) (Tab. XXXIV. A.). 



Resembling Z .viridissimus but more slender ; leaves smaller, 

 erecto-patent, straight or almost so ; nerve a little more distinct ; 

 cells rather larger, more distinct, more strongly papillose. Seta 

 very slender, as long as in that species ; capsule smaller, with a 

 longer, more distinct neck. Peristome double, small and fugacious ; 

 outer of 8 short obtuse teeth, in pairs ; inner of 8 delicate, 

 fugacious processes. Dioicous. 



Hab. Trees, rare. Fr. early summer. 



According to Boulay the characters, other than that derived from the presence of 

 a peristome, are inconstant, and he makes Z, conoideus a sub-species of Z. viridissimus. 

 It is to be remembered too that very faint rudiments of a peristome have been found 

 occasionally in the latter species. On the whole, however, I have preferred to follow 

 the usual arrangement and separate the two ; not only on the ground that the presence 

 of a well developed, double peristome, is a character of some considerable import- 

 ance, but also on account of the general consensus of opinion, which is borne out by 

 the specimens I have examined, in favour of a generally more slender habit on the 

 part of Z. conoideus, a smaller capsule with more distinct neck, straight leaves, and 

 larger and more distinct cells. 



5. Zygodon Forsteri Wils. (Bryum Forsteri Dicks.) 

 (Tab. XXXIV. B.). 



In small compact dark green cushions, about £-inch high or 

 less, with pale radicles below. Leaves erecto-patent, when dry 

 very slightly twisted, oblong-lanceolate or slightly obovate-spathu- 

 late, apiculate, not carinate ; margin plane, entire ; nerve strong, 

 reaching to the apex ; basal cells lax, hyaline, rectangular, with 

 thin walls, the upper hexagonal, or quadrate-hexagonal, much 

 larger than in the previous species, 16-20 p in diameter, deep 

 green with chlorophyll and with highly pellucid cell-walls, not 

 papillose. Seta stout, reddish brown. Capsule reddish or 

 yellowish brown, thick-walled, long-necked, narrowly pyriform or 

 oblong-pyriform, when ripe narrowed above, and slightly con- 

 tracted below the mouth, when old becoming narrower, strongly 

 8-ribbed ; lid shortly rostrate, oblique ; peristome double, outer 

 in 8 pairs, which again are somewhat coherent two by two, 

 strongly reflex ed, inner of 8 subulate processes. Autoicous. 



