Reviews — Nicholson's Tabulate Corals. 565 



the number of mesenteries in the living animal, it is difficult to see 

 how Halysites can be regarded as an Alcyonarian, this group having 

 only eight mesenteries. 



The family of the Thecidae comprises merely the single genus 

 Thecia, Edw. and H., with very peculiar characters, now, for the first 

 time, made known from microscopic sections. There are two kinds 

 of corallites ; the larger, though well defined, have no distinctive 

 bounding walls, and the interspaces between these are occupied by 

 very small tubular corallites, doubtfully tabulate, but with well- 

 defined walls. There are also horizontal canals connecting the 

 larger corallites. The family is regarded as a special group of the 

 Alcyonaria. 



The important family of the Helioporidae mostly comprises the 

 Palaeozoic genera Heliolites, Dana, Plasmopora, Edw. and H., Propora, 

 Edw. and H., Pinacopora, Nich. and Eth. jun., and Lyellia, Edw. 

 and H. ; the Cretaceous genus Polytremacis, D'Orb., and the recent 

 Heliopora, De Blain. These various genera are included in this 

 family from the supposed correspondence of their fossil structures 

 with the corallum of the existing Heliopora, the animal of which has 

 been proved by the researches of Mr. Moseley to be a true Alcyonarian 

 Zoophyte, furnished with eight mesenteries, and eight pinnately- 

 fringed tentacles. It appears to us, however, that there are con- 

 siderable differences between the corallum of Heliolites and its 

 allied Palaeozoic forms, and the recent Heliopora ccerulea, sufficient 

 to throw considerable doubt as to the propriety of associating them 

 in a single family of Alcyonaria. We regret that Dr. Nicholson has 

 not subjected the modern corallum of Heliopora to the same critical 

 examination which he has bestowed on the Palaeozoic Heliolites, 

 before accepting the classification of Mr. Moseley, and we will 

 venture to point out what appear to us some of the points of 

 difference. In the first place, the larger corallites or calicles of 

 Heliopora coerulea do not appear, from Mr. Moseley's account, to 

 possess any distinctive proper wall. He says: 1 ''New calicles are 

 formed by the junction of a number of tubes around a central tube 

 or tubes arrested in growth, which form a base. The outer walls 

 only of the surrounding tubes continue to grow, and form the 

 lateral wall of the caliche. The newly-formed caliche thus has 

 tabular prolongations at its base, and the so-called septa are, in the 

 main, due to the circumstance that the wall is composed of a series of 

 curved outer walls of tubes." Our own observations of H. coerulea 

 fully confirm the correctness of the above description. Now, so far 

 as we are acquainted with Heliolites and its allied Palaeozoic genera 

 which have been placed with Heliopora, there is not a single species 

 in which the tubes of the larger corallites are formed in a similar 

 manner to those of Heliopora, but in all there is a distinct proper wall 

 to the larger corallites. Again, with regard to the septa of Heliopora, 

 these, according to Moseley, are in the main due to the curved outer 



1 "We quote from the Report given in the Ann. and Mag. of Nat. History, Feb. 

 1876, p. 147, et. seq., " On the Structure and Relation of certain Corals, etc.," by H. 

 N. Moseley, M.A., F.R.S. 



