210 ARCHER, ON A NEW SPECIES OF MICRASTERIAS. 



Locality. — A large pool near tlie '^ Old Gable," Feather- 

 bed jNIouiitain, and sparingly elsewhere in the vicinity. 



Measurements. — Length of frond, —^ ; breadth of frond, 

 TTir '} gi'eatest depth of frond, -^-4--, inclusive of the projections; 

 exclusive of the projections, -^^ of an inch. 



General description. — Frond orbicular, smooth, segments 

 in front view five lobed, having the lateral lobes dichoto- 

 mously incised, furnished at the base with three conspicuous 

 hollow projections or protuberances, the middle one conical, 

 rounded ; the outer distant from each other rather less than 

 one-third the diameter of the frond, tapering, curved, some- 

 what elongate, emarginate at the extremities, sometimes 

 with a tooth on the upper margin, laterally divergent from 

 each other, but approximate to those of the opposite segment; 

 basal lobes with two little apiculate, conical elevations on the 

 surface, apparent only on the emptj^ frond, their apices 

 directed outwards, equidistantly placed at the base of each 

 of the primary subdivisions of the lobes, and on a level with 

 the extremity of the primary incision; middle lobes with 

 three similar elevations, two placed at the base of each of the 

 primary subdivisions, on a level with the extremity of the 

 primary incision, and the other placed at the base of the 

 lobe, distant about as far beneath the other two as they ai'c 

 from each other, the two elevations of each of the basal and 

 the two outer of each of the middle lobes forming regular 

 series semicircularly disposed ; end lobe with two similar 

 elevations, one placed beneath the other, the outer somewhat 

 within the semicircular series of elevations of the basal and 

 middle lobes — the inner at the base on a level, and horizon- 

 tally forming a nearly straight series of three, with the inner 

 elevation of each of the middle lobes. (Plate XII, fig. 2.) 

 Basal and middle lobes mostly thrice dichotomous, the 

 primary incisions deep, linear, about one half the depth of 

 the lobes ; the secondary incisions linear, about one third 

 the depth of the primary ; tertiary incisions shallow, trian- 

 gular or rounded, scarcely one half the depth of the secondary; 

 the ultimate subdivisions bidentate. Sometimes the tertiary 

 incisions are obscure or obsolete, M'hen the basal and middle 

 lobes are therefore but twice dichotomous, and the ultimate 

 subdivisions then mostly tridentate or quadridentate. End 

 lobe narrow, with nearly parallel sides at the base for nearly 

 half its length, thence suddenly widening, wholly included, 

 acutely emarginate at the end at the middle ; outer margin 

 concave at each side close to the notch, beyond which it is 

 convex, its angles acute. (Figs. 1, 2.) In side view the 

 frond rather more than three times longer than broad, seg- 



