46 PERMIAN FOSSILS. 



concluded to be the homologues of the gemmuhferous vesicles often seen overlying the 

 cellule-apertures of Bryozoic Corals. 



As the mode of formation of the gemmuhferous vesicles is not generally known, a 

 few particulars on the subject, as supplied by an examination of some recent forms, 

 may not be altogether inappropriate. In Masmopora {Beaniana) they are prominent 

 and spherical: their basal or attached portion, somewhat cup- shaped, is first formed; next 

 their lateral margins, which arch over to within a short distance of each other, leaving 

 a narrow longitudinal fissure. In Escharina the vesicle in its early stage resembles the 

 latter ; its lateral margins, however, do not remain separated, but become confluent, 

 forming an irregular dome-shaped appendage : whether the foramina with which its 

 outer or convex wall is furnished, answer the purpose of an opening, or there is one on 

 its proximal or inferior part, that is, in proximity to the upper lip of the cellule- 

 apertures, I am not enabled to say. In Cellaria salicornia the gemmuhferous chamber 

 is neither prominent nor spherical, but always remains sunk in the substance of the 

 Coral, forming a cup-shaped cavity, as it evidently is in Thamniscus dubius : at first 

 there is a difl&culty in distinguishing it from the adjacent inferior cellule-aperture ; 

 afterwards, however, it becomes gradually separated from the latter by the interposition 

 of a narrow calcareous dissepiment ; and its opening, at first circular, is gradually 

 converted into a transverse linear fissure. 



Besides the gemmuhferous chambers in Thamniscus dubius, but where they are 

 absent, there is occasionally seen what may be termed an accessory vesicle on both sides 

 of the distal lip of the cellule-apertures, as represented in Plate V, fig. \\ a, which 

 reminds one of a similar structure a little below and on both sides of the proximal 

 lip of the cellule-apertures in certain Escharinas. 



In some specimens of Thamniscus dubius, as in the one represented under figure 12, 

 Plate V, the proximal lip is furnished with a denticle-like process, which occasionally 

 varies a little between the right and left of its usual position.^ In a few instances I 

 have observed casts of the same appendage, showing it to have been hollow, and 

 homologous with the hollow mucronate process similarly situated in Cellepora Skenei, 

 in which the mucro is furnished with two foramina on the upper side and near the 

 base. Masmopora Beaniana possesses a similar process, but it is foraminated at 

 the point. I have not been able to discover, as yet, any foramina in the corresponding 

 part of the fossil. 



The first synonym quoted for this species is explained by the fact, that Schlotheim 

 imagined its branches to be the arms of a Cyathocrinus ramosus incrusted with 

 a Thamniscus dubius. 



Thamniscus dubius is not a common Coral, though it is pretty generally, distributed. 

 It occurs at Tunstall Hill, Ryhope Field-house Farm, Castle Eden Dene, Humbleton 



' In the impression of the fossil represented in Plate V, fig. 1 1 e, there is a pit or depression of the 

 same appendage under some of the cellule-apertures. 



