52 DUBLIN NATUEAL HISTOET SOCIETY. 



ginal, and in pairs, and in the central projection being not granulate ; 

 but it differs in its far more minute size, and in its segments being 

 four- sided, not reniform or sub-hexagonal, and in its spines being short, 

 and minute and straight, not elongate and usually curved, and in its 

 constriction not forming a linear notch. With the other species named 

 (var. /3) this form agrees in its trapezoid segments, and in the number 

 and disposition of its spines, but differs in possessing the central frontal 

 projections, which are absent in the species alluded to, and which cir- 

 cumstance, I thitrk, should place it out of the genus Xanthidium. The 

 form now under consideration differs besides 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 ; in the ends being truncate, not rounded ; 

 and in the extremities in the end view being blunt, not rounded. JN"ot- 

 withstanding, therefore, considerable similarity in the general outline 

 between the present species and Arthrodesnms 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 hifidus (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 William 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. 



The Meeting then adjourned to the month of ]S"ovember. 



