dredged up from the Gulf of Man aar. 441 



Melobesian nodules, which, being polytrematous (literally), 

 possessing fragmentary sponge-spicules in its interior, and 

 presenting the same red colour as P. miniaceum, I at first 

 thought to be another new species ; but on further examination 

 it was found to be a reptant Tubipora so like T. musica that, 

 but for its stoloniferous growth and consequent modifications, 

 together with the presence of the fragmentary sponge-spicules 

 incorporated with its corallum, it might be considered identi- 

 cal. This species I shall designate Tubipora reptans ; and, 

 although belonging to the Polyp ifera, it will be described here 

 for convenience, as before noticed, on account of the great 

 resemblance to Polytrema just mentioned. 



Here also I would take the opportunity of introducing 

 another species of Polytrema, which accidentally came into my 

 possession, in a rolled state, having probably been picked up 

 upon some beach ; but where, I am ignorant. Imperfect as it 

 is, however, it is remarkable for its size and other charac- 

 teristics : with a Polytrema-like structure and pink colour, it 

 is so much larger and so differently formed from any hitherto 

 published, that it must be considered a new species, which 

 I propose to designate (also in reference to its form) P. 

 mesentericum. 



These species will now be respectively described, beginning 

 with 



Polytrema cylindncum, n. sp. (PI. XVIII. fig. 1, a-g.) 



Erect, cylindrical, consisting of a thick round pillar deve- 

 loped from a slightly expanded base, dichotomously divided 

 at the free end into two short thick branches, which are equal 

 in length and opposite, terminating respectively in an expan- 

 sion, from the centre of which radiate a number of more or 

 less fragmentary sponge-spicules. Consistence stony. Colour 

 red, cinnamon, or crimson; translucent (PL XVIII. fig. 1). 

 Surface of the pillar and branches uniformly divided into gentle 

 convexities, pierced with foramina which are sunk into a sub- 

 reticulated lineation whose interstices vary in prominence with 

 the development of the organism — being most prominent in the 

 oldest parts, and vice versa (fig. 1, e) ; ends of the branches 

 rendered irregular by the outgrowth of cells, which are other- 

 wise hidden in the pillar and branches, as will appear pre- 

 sently. Cells at the ends of the branches bearing respectively 

 a large aperture, similar in form, position, and margination to 

 that of the cells of Planorbulina (fig. 1, c), which they further 

 resemble in the form of their pore-tubulation ; divided into 

 two groups by a central rima, presenting a number of aper- 

 tures, out of which project the fragmentary sponge-spiculea 



