ARCHEll, ON A NEW SPECIES OF MICRASTERIAS. 241 



ments someAvhat pyramidal; in general outline inflated at 

 the base, sides coneave immediately above ; again dilated 

 about half way up, the central lateral projections directed 

 upwards, with a sinus on each side immediately above ; sides 

 again contracted, and above again exhibiting a lateral pro- 

 jection at each side ; end ti'uncate, the upper edge {in empty 

 frond) showing the extremities of the various lobes and sub- 

 divisions. (Fig. 3.) In end view the segment narrow-lan- 

 ceolate, presenting at each side, at the middle, the central, 

 rounded basal projections, and beyond it, at each side, the 

 pair of large, conspicuous, curved, emarginate, divergent pro- 

 jections, the general outline presenting a doubly hastate 

 appearance, the rounded projections intervening, the upper 

 edge (in empty frond) showing the extremities of the various 

 lobes and subdivisions, the lobes presenting a somewhat ob- 

 campanulate outline, with a lateral minute projection at each 

 side, its apex directed outwards. (Fig. 4.) In transverse 

 view of a segment it is lanceolate, presenting much the same 

 outline as the end view, save that, the outer edge being turned 

 away from the observer, the subdivisions of the lobes are not 

 now apparent, the foramen and basal projections being now 

 uppermost, and in this position very strikingly displayed. 

 (Fig. 5.) Endochrome rich green, sometimes not reaching 

 to the margin of the frond, and thus leaving a hyaline border, 

 and containiug numerous conspicuous, rounded, scattered, 

 large granules. 



Plate XII, fig. 1, front view ; fig. 3, side view ; fig. 4, 

 end view ; fig. 5, transverse view. All magnified 200 dia- 

 meters. 



This complex form is very pretty, but, without obtaining a 

 side and end view of an empty frond, is difficult to under- 

 stand. Indeed, the outer semicircular series, and inner 

 series of three little apiculatc elevations, are not discernible 

 when the frond contains its endochrome ; but the large, 

 curved projections at the base of the segments, even in front 

 vicAv, are readily seen, and under a low power, owing to the 

 greater depth and consequent greater opacity, appear like two 

 darker portions at the base of each segment ; by focusing 

 under a higher power, they are most easily made out ; they 

 are quite conspicuous on the empty frond. (Fig. 2.) That 

 these curved projections are hollow is indicated by my having 

 seen, in an empty segment, an infusorium making its Avay up 

 into and down again from one. On the empty frond, also, 

 the superficial apiculatc projections are readily seen ; occa- 

 sionally one appears emarginate or divided, showing a double 

 apiculus. It is not, however, until an end or transverse view 



