,S0 Proceedings of the Royal Irish Academy. 



elongated veiTucae. The coeueuchyma is thick, with an external layer which 

 contains simple and double clubs. 



Scirpearia. — The colony is simple, with a cylindrical calcified axis and thin 

 eoeneuehyraa. The polyps are seated in two longitudinal rows on each side 

 of the stem. The spicules are double-clubs and spindles. 



Scirpearella. — The colony is simple or very feebly branched. The axis is 

 calcareous, brittle, smooth or grooved. The polyps are arranged in rows or 

 spirals, retractile, with more or less prominent verrucae. The coenenchyma is 

 moderately thick and finely granular. The spicules are spiny spindles and 

 double-clubs. 



Ellisella. — The colony is simple or diehotomonsly branched, with a thick 

 coenenchyma, and slightly developed verrucae, which are disponed in two rows 

 on the axis. The coenenchyma contains both doulile-clubs and spindles. 



Ctenocella. — The colony is branched in one plane, and so that all the 

 simple twigs arise in an ascending order from the upper surface of the stem. 

 The verrucae are short on two sides of the twigs. There are distinct median 

 furrows. The spicules are mostly double-clubs ; those of the polyp-calyces 

 are, according to Eidley, somewhat different from those of the coenenchyma, 

 being longer and provided with two, often three whorls of tubercles. The 

 inner whorls so approach in the middle of the spicules, that the median naked 

 zone, which is characteristic of the spicules of the coenenchyma, is here absent. 



Nicella. — The colony is upright, branclied, with a thin coenenchyma, and 

 protruding verrucae, which arise perpendicularly, and appear to be terminally 

 truncated. The polyps arise from either side of the stem and branches, 

 leaving a middle space free. The spicules form a cortical layer of small 

 double-clubs, and an internal layer of long densely warty spindles. 



An examination of these diagnoses reveals the fact that we have here to 

 deal with three distinct groups. The first of these is represented by the 

 various species of the genus Juncella, and is characterized by the fact that 

 its spicules include simple clubs. The second is restricted to the genus 

 Nicella, and is distinctly separated by the character of its spicules, which 

 include small double-clubs and long, densely warted spindles. 



The thii'd comprises Ellisella, Scirpearia, Scirpearella, and Ctenocella, which 

 agree in having neither clubs nor long spindles, but whose spicules all include 

 double-clubs. These distinctions may be tabulated thus : — 



A. Spicules include clubs (Juncella). 



B. Spicules do not contain clubs — 



(1) Spicules include extremely elongated spindles (Nicella). 



(2) Spicules do not contain elongated spindles (Ctenocella, 



Ellisella, Scirpearia, Scirpearella). 



