CLASSIFICATION. 21 



another, and there is no evidence of the existence of " mural 

 pores" in such parts of their extent as they may be actually 

 contiguous. The septa are reduced to marginal striae ; and 

 horizontal complete tabulae are known to be present in certain 

 forms, though they have not yet been detected in others. 



It is well known that the basal and young portion of the 

 corallum of Syringopora is in the form of a creeping stolonifer- 

 ous expansion, almost undistinguishable from the adult colony 

 of Aulopora in appearance. This fact has led high authorities to 

 the belief that the genus Aulopora has no existence, and that 

 it is merely based upon young colonies of Syringopora. This 

 view of the subject appears to me to be untenable with our 

 present knowledge and I think Aulopora to be really quite 

 distinct from Syringopora. I base this belief upon the fact 

 that the corallum in Aulopora is always prostrate and parasitic, 

 never becoming erect ; that there are no traces of hollow con- 

 necting-processes between the corallites ; and that the tabulae 

 (when known to be present) are horizontal, or if infundibuli- 

 form, do not give rise to an axial tube. There is also the 

 strong geological argument for the distinctness of the genus, 

 that formations abounding in Syringopora (such as the Car- 

 boniferous Limestone series of Britain) are almost (in most 

 places wholly) destitute of Aulopora; whereas the latter are 

 extremely plentiful in deposits (such as the Devonian Limestone 

 of Gerolstein in the Eifel) in which Syringopora are almost 

 or quite unknown. The genus Cladochonus, M'Coy (which 

 is apparently the same as Pyrgia, Edw. and H.), seems to 

 comprise forms of different affinities. Some of the species 

 seem to be tabulate, with horizontal tabulae, and may perhaps 

 be identical with Aiilopora proper. The Cladochonus crassus 

 of M'Coy, however, has an entirely peculiar internal structure, 

 which must remove it altogether from the Auloporida. 



VII. HALYSITID^E. In this group, typified by the common 

 " Chain-corals," the corallum is composed of long cylindrical 

 corallites, united with one another successively on opposite 

 sides of the tubes, so as to give rise to flattened laminar expan- 



