494 125. Pyrenula. 5. IDIOTHALAMEiE. Pl.cell.aph . 
3. Pyrenula nigrescens . Blackish nut-moss. 
Crust tartarlike, slightly cracked, uneven, brownish- 
black ; apothecia enlarged at bottom, depressed, rather 
wrinkled, closed, strictly surrounding the greatest part of 
the prominent, nipplelike thalamium. 
Lichen umbrinus, Achar. Prod. 14; Engl . Bot. 1499. 
Verrucaria umbrina, Achar. Melh. 122. 
Verrucaria antiquitatis, Florke in Berl.Mag. 1807, 1, 17. 
Pyrenula nigrescens, Achar. Syn . 126. 
On stones. 
V. 126. THELOTREMA. Acharius. Open-iv art-moss. 
Thallus crustlike, cartilaginous, flat, expanded, adnate, 
uniform; apothecia wartshape, formed of the thallus, open, 
bordered; thalamium single, enclosed in the wart; peri - 
thecia double; one halved above, thick, black, seldom want- 
ing ; the other very thin, membranaceous, sometimes alone, 
or broken above ; surrounding a compressed, cellular, 
slightly streaked nucleus, placed in the bottom of the wart. 
1. Thelotrema lepadinum. Barnacle open-wart-moss . 
Crust smooth, whitish ; apothecia smooth, nearly conoid, 
edge of the opening thin, simple, rather bent inwards, con- 
tracted ; bottom covered with a membrane which becomes 
torn. 
Lichen inclusus, Engl. Bot. 678. 
Lichen lepadinii3, Achar. Prod. 30. 
Thelotrema lepadinum, Achar. Meth. 132 ; Lich. 312. 
On the bark of trees. 
2. Thel. exanthematicum. Eruptive open-wart-moss . 
Crust rather tartarlike, thin, not cracked, greyish ; apo- 
thecia convex, half sunk, whiter ; opening half closed, 
radiately cracked, becomes gaping ; bottom veiled, yellow- 
ish flesh-colour. 
Lichen volvatus, Vi liars Delph. 55. 
Lichen exanthematicus, Smith in Lin. Tr. 1,81 ; Engl. Bot. 1184. 
Urceolaria exanthematica, Achar. Meth. 146. 
Thelotrema exanthematica, Achar. Lich. 313. 
On rocks, especially limestone. 
Halit peculiar, but seems most referable to this genus. 
3. Thelotrema agelceum. Inelegant open-wart-moss . 
Crust white, rather powdery, or sprinkled with very 
small granules or soredia; apothecia pressed close, few, 
slightly sunk in the crust. 
