206 PROCEEDINGS OF THE AMERICAN ACADEMY 



All the European species, and indeed all that belong to the genus 

 (as revised by Fries) in the last general work of Acharius (Synopsis), 

 occur with us, with several others. It is difficult to define strictly the 

 limits between the foliaceous species of Cetraria and some Parmelise 

 of the subsection Imbricaria ; and in his Flora Scanica, Fries has sug- 

 gested the possibility of extending Cetraria to include most or all of the 

 Imbricarise. But the genus, as limited in the Lichenographia Euro- 

 psea, seems a natural one, and well distinguished from Parmelia. 



§1. C artilagine<2,Fr, Thallus cartilagineous, suberect. 



1. C. tristis, Fr. Thallus fruticulose, horny-cartilagineous, rigid, 

 solid, distichally dichotomous, pitch-black, branches fastigiate, terete ; 

 apothecia terminal, plano-convex, disk fuscous-black. Fr. Lichenogr. 

 p. 34. Cornicularia, Ach. 



Alpine and arctic rocks. Arctic America, Rich. 



2. C. odontella, Ach. Th. fruticulose, rigid, solid, subcompressed, 

 palmate-ramose, dark-brownish-chestnut, branches plane, dentate (not 

 ciliate-spinulose) ; apoth. terminal, plane, disk fuscous. Fr. Lichen- 

 ogr. p. 35. 



Stones and moist rocks in alpine districts. Newfoundland, Despreaux 

 in herb. Deless. ! Bory in herb. Kunth ! fertile. Northward to Arctic 

 America, Herb. Hook. ! Melville Island, JR. Br. (Parry's First Voy.). 



3. C. aculeata, Fr. Th. fruticulose, rigid, subfistulous, lacunose- 

 compressed, very much and irregularly branched, dark-brownish-chest- 

 nut, branches divaricate, black-spinulose ; apoth. terminal, peltate, den- 

 ticulate, disk of the same color. Fr. Lichenogr. p. 35. Cornicularia, 

 Ach. 



On the earth in alpine and subalpine districts. White Mountains, 

 fertile. Northward to Arctic America, jR. Br., Hook. ! 



4. C. Richardsonii, Hook. Th. subfoliaceous, canaliculate, divari- 

 cate-bipinnatifid, naked or sparingly black-denticulate, dark-chestnut ; 

 apoth. marginal, subpedicellate, margin granulate or irregular, disk 

 yellowish-brown. Hook, in Frankl. Narr. p. 761, & Icon, t. 31. 



Barren grounds north of Great Slave Lake, Rich. (herb. Hook. ! & 

 herb. Grev. !). Prostrate. 



5. C. Islandica, Ach. Th. subfoliaceous, sublinear, canaliculate, 

 ciliate-spinulose, olivaceous-chestnut ; apoth. obliquely scutellate, ad- 

 nate to the upper side of the lobes, very entire, disk dark-chestnut. 



