336 PROCEEDINGS OF THE 



clustered on Actinocrinus — which is rare — neither worn nor eroded, 

 and otherwise specially marked. One has first accommodated a 

 Crania^ subsequently the clustered coralloid under consideration ; 

 another was first the resting-place of a Crania^ then of the coralloid, 

 and afterward of the basement portion or foot of a young crinoid 

 (specimen d). What a throng of life ! More remarkable still, 

 the third is an example of a cluster of great rarity, and appears to 

 have been constructed on a living crinoid ! This specimen is 

 most instructive ; the stem had evidently continued to grow, 

 while the spot occupied by the coral patch seems to have been 

 arrested in growth (specimen e). This specimen, glanced at and 

 put aside for examination during the past sixty years, is the only 

 example noted as bearing evidence that the polypi engaged in the 

 process of construction adopted a living encrinite as the field on 

 which to labour. Two other specimens are notable, because 

 rare. On short stems of Poteriocrinus, the cluster on each covers 

 the entire joint-disc or end of ossiculi, passes over the edge on to 

 the stem, encircling what may be supposed to have been the only 

 exposed part, the other end having been fixed in the mud 

 (specimen f). Hence it is certain that Stenopora tumida did 

 encircle stems when placed favourably for the operation. How 

 this coralloid clung so closely to old worn stems of Poteriocrinus 

 crassus as a building station may be a question difficult to solve. 



2. Archaeopoi^a nexilis. — Of this polyzoon thirty specimens were 

 likewise examined, all — with rare exceptions — attached to small 

 and short well-preserved or unworn crinoid stems. . Fifteen of 

 that number encircle, but do not in any instance pass on or over, 

 the ends of the stems (specimens A, B, c). Twelve are on 

 Poteriocrinus, two on PJioclocrinus, and one on Actinocrinus. 

 Fifteen others do not entirely complete the encircling process, nor 

 do they pass over or on the ends of the stems ; of which number 

 eleven are on Poteriocrinus, three on Actinocrinus, and one on 

 Bhodocrinus. The fabric of this species is thin, comparatively 

 equal or smooth, not exceeding in thickness a calling card on an 

 average, and in every instance that structure, when the crinoid on 

 which it is constructed has been broken, or at severed joints, is 

 found irregularly fractured. Encircling of the stems, and their 

 freshness, implies that the crinoids had been erect during the 

 operations of the special polypi ; and it may be farther implied 

 that the crinoids lived while the construction proceeded. 



