HICKS; ON GONID1A OF LICHENS. 239 



agrees in its trapezoid segments, and in the number and dis- 

 position of its spines, but differs in possessing the central 

 frontal projections, which are absent in the species alluded to, 

 and which circumstance, I think, should place it out of the 

 genus Xanthidium. The form now under consideration also 

 differs from that alluded to in having its margins straight, 

 not concave ; in its spines being minute, not elongate ; in 

 the segments, in side view, which is less compressed, being 

 sub-orbicular, not elliptic j in the ends being truncate, not 

 rounded ; and in the extremities in the end view being blunt, 

 not rounded. Notwithstanding, therefore, considerable simi- 

 larity in the general outline between the present species and 

 Arthrodesmus octocornis, var. /3, I cannot suppose they can 

 be identical. The latter I have not myself met with in this 

 country, but var. a is not uncommon. However, I prefer to 

 follow Brebisson, and to place both those forms in the genus 

 Arthrodesmus, though, perhaps, Jenner's suggestion to form 

 a new genus for them, including, of course, Arthrodesmus 

 bifidus (Breb.), would, after all, be the better course. Certain 

 it is that the plant now described is an unquestionable 

 Xanthidium. 



I imagine the initials on the slide above alluded to must be 

 those of the late Professor \Yilliam Smith; it is, however, in 

 any case by no means an inappropriate, though but a small 

 and very inadequate, mark of respect to dedicate this species, 

 which I believe to be very distinct, to his memory. 



Coxtributions to the knowledge of the Development of the 

 Gonidia o/Ltchens, in relation to the Unicellular Alg^e, 

 fyc. By J. Braxton Hicks, M.D. Lond., F.L.S., &c. 



Fasciculus 1. 



It needs no remarks of mine to point out the extreme 

 ambiguity which exists in regard to the arrangement of both 

 the species and genera of the unicellular algae and their kin- 

 dred organisms. Perplexing to the last degree to the older 

 student, to the novice they are bewildering, and highly un- 

 satisfactory to all who, allured by their simplicity of struc- 

 ture, have been desirous of studying Nature on her protophytic 

 threshold. 



However, within the last few years an opinion, based on 



