Appendix to Part I. 1 8 1 



of the characters just noticed, but more generally the impressions 

 display scarcely a trace of any other structure than longitudinal 

 rows of circular mouths. 



On the inner layer of the non-cellular surface, twenty well- 

 marked parallel fibres, with intermediate narrow grooves or corre- 

 sponding casts, may sometimes be detected, and the number is 

 always considerable. The mode of preservation did not permit the 

 true nature of the fibres to be discovered, but in consequence of 

 what has been noticed in other species, it is inferred that they are 

 tubular. Their range is considerable, but in the specimen, which 

 exhibits their structure most fully, they are frequently cut off by 

 circular foramina. Their perfect surface is minutely granular. 

 The outer layer, or back of the branches, is composed of an uniform 

 crust without any indications of fibres, but covered with numerous 

 microscopic papillae, and corresponding pores penetrating the sub- 

 stance of the layer. 



The onlyindications of gemmuliferous vesicles, are small circular 

 pits occasionally situated over the mouth, and agreeing in position 

 with the vesicles, which in other cellular genera, have been con- 

 sidered as gemmuliferous. In the Russian specimen before alluded 

 to, casts of similar pits are very uniformly distributed between the 

 casts of the mouths. 



The youngest state of the coral has not been noticed, nor have 

 any marked changes incident upon age, except the gradual thicken- 

 ing of the non-cellular surface, by the coating over of the fibrous 

 layer. 



The matrix of the specimens is a dark gray splintery or an earthy 

 limestone. 



2. Fenestella inters at a, sp. n. 



Cap-shaped ; celluliferous surface internal; branches dichotomous, 

 compressed, breadth variable; meshes oblong, narrow; rows of 

 cells 2 — 5, divided by longitudinal ridges ; transverse connecting 

 processes short without cells ; non-cellular surface, inner layer, 

 sharply fibrous, outer layer, minutely granular. 



By the delicacy of its structure, this species is easily distinguish- 

 able from Fen. ampla • and in the rows of cells varying from two 

 to five, as well as in their mode of development, there are further 

 well-marked differences. It appears to have attained considerable 

 dimensions, fragments having been noticed an inch and a-half in 

 length and an inch in breadth. 



The branches vary in width, swelling cut gradually towards the 

 bifurcations, but without any alteration in the form or size of the 

 meshes ; and as far as the state of the specimens will permit an 

 opinion to be formed, no marked changes occurred during the deve- 

 lopment of the cup, except one about to be noticed. On the cellu- 

 liferous surface of the branches, considerable, but uniform, altera- 

 tions take place between the successive bifurcations. For a short 



