186 Pv. r. TOMES ON" MABKEPORARTA 



distinct from Comoseris. TJie only distinction is the length of the 

 ridges hounding the calicinal valleys." Prom this concluding state- 

 ment, which is here printed in italics by me, I feel myself compelled 

 to express a most unqualified dissent. Wishing, however, to make a 

 more critical examination of the ridges of the calicular surface of 

 Comoseris., with a view to the determination of the question whether 

 they have walls or not, I have made careful examination of a great 

 many specimens of Comoseris irradians, from the Corallian of Steeple 

 Ashton and the Boulonnais, and of Comoseris vermicularis from the 

 Great Oolite of the neighbourhood of Bath. The results of this 

 renewed examination I will now proceed to give, premising that 

 the time and trouble will not be wasted which places on a sounder 

 footing our knowledge of the forms now under consideration. 



The most superficial observation of well-preserved specimens of 

 Comoseris irradians will afford sufficient evidence of the distinctness 

 of the ridges or collines which divide the upper surface of the corallum 

 into segments. When compared with the intervening calicular sur- 

 face these collines (PL Y. fig. 24) have a character of their own, 

 quite independently of the calicos, and are clothed with costae, very 

 little resembling the septal costae in connection with the calicos. 

 For instance, on some of the collines the costae on the one side do not 

 correspond with those on the other side, but alternate with them, 

 just as do the septa of contiguous calicos of many compound corals, 

 such as those of some species of /sas^rtra, and they are consequently very 

 suggestive of a concealed wall. Accordingly, in worn specimens a 

 very distinct and continuous line is sometimes observable, simulating 

 a true wall ; but sometimes it has a serrated or zigzag course, and 

 then presents so much the appearance of the inflected walls between 

 the lobes of Phyllogyra as to suggest a similarity of origin. With- 

 out entering further into the question of the nature of the wall 

 observable in the collines of Comoseris, I may venture to assert that 

 no such wall, whatever may be its nature, exists in Oroseris. To 

 this I shall again refer. I may add, as characteristic of the genus 

 Comoseris., that the calices are scattered over the surface between 

 the ridges, and never developed in lines as thej'^ commonly are in 

 Oroseris. Sometimes the collines are very frequent, and there is 

 only space for one row of calices between them. But when the 

 former widen out, the calices spread out also, and the uniformity 

 of the line is broken. This is very observable in both Comoseris 

 irradians and Comoseris vermicularis (PI. Y. fig. 25). 



Fortunately for the examination of the genus Oroseris there is a 

 species commonly occurring in the Great Oolite of Bath, which, 

 when rubbed down, shows the structure of the calices very satis- 

 factorily. In this species the calices are so near together in the 

 lines, and the lines themselves have so much of a radiate direction, 

 that they can only have been the result of direct gemmation from 

 the inner calices outwards, without the interposition of septal costas. 

 The so-called ridges laterally bounding the lines of calices are really 

 nothing more than ordinary septal costae, such as are visible between 

 the calices of many species of Thamnastrcea. The Thamnastrcea 



