332 Dr. H. A. Nicholson on the Minute 



hitherto (so far as I am aware) been noticed as occurring in 

 Heteropora. 



The above are the most important structural features which 

 had been brought to light by the study of the fossil species of 

 Heteropora ; but our knowledge of the anatomy of the genus 

 has been greatly extended by the investigation of recent 

 species by Mr. Waters and Prof. Busk, as already referred to. 

 The leading additional character which has been thus brought 

 to light is that the walls of the zooecia and cancelli (in the 

 outer portion of their course) are perforated by numerous 

 canals, which open into the cavities of the tubes by well- 

 defined circular openings, thus placing contiguous tubes in 

 direct communication. 



Having now shortly passed in review some of the more 

 important characters of Heteropora, so far as our present 

 inquiry is concerned, I may next give a short account of the 

 general features of H. neozelanica, Busk, before describing in 

 greater detail its minute internal structure. The zoarium of 

 this species (fig. 1, A) is " erect, composed of short divergent 

 branches springing from a short thick stem, and soon dividing 

 once or twice dichotomously, and terminating in blunt rounded 

 extremities. The diameter of the primary branches is '2 inch, 

 and of the terminal ones about # 1 to *15 inch. The surface 

 presents orifices" (see fig. 1, B and C) "of two kinds, though 

 scarcely distinguishable in size. The larger ones, in the 

 older parts of growth, have a slightly raised peristome and 

 are quite circular; the others {cancelli), disposed more or less 

 regularly round these, generally to the number of seven or 

 eight, are more or less angular, and the border of the opening 

 is never raised" (Busk, loc. cit.). 



Mr, Busk considers his H. neozelanica to be probably 

 distinct from H. pelliculata, Waters, on the ground (1) of 

 certain differences in the general form of the polyzoary, and 

 (2) of the absence in the former of any external calcareous 

 pellicle covering the surface, though there exists, in perfectly 

 preserved parts of the specimen described, a thin chitinous 

 covering closing the mouths of the tubes. Mr. Waters, as 

 before remarked, is inclined to believe that the two forms are 

 identical, in which case the name H. neozelanica will have to 

 be abandoned. In fig. 1, B and C, I have figured the two 

 states of the surface which my specimen of H. neozelanica 

 exhibits, one of these being a reproduction of the excellent 

 figure given by Prof. Busk {loc. cit.). I have also reproduced 

 the figure given by Mr. Waters of the surface of H. pellicu- 

 lata, as it shows characters which merit a moment's attention 

 in this connexion. The left-hand portion, namely, of this 



