CLASSinCATOKY POSITION OF SOME MADKEPORARIA. 137 



genus by Milne-Edwards and Jules Haime, namely Clausastrcea, 

 the form being O. Pratti (now Plerastrcea Pratti, Ed. & H.). This 

 species was figured on the same plate as Isastrcea Conyhearii by 

 Milne-Edwards and Jules Haime. The only defective part of the 

 di'awing of Clausastrcea Pratti, which was afterwards placed in the 

 genus Plerastrcea, is owing to the bad printing. The print gives 

 the notion of a solid columella, and this is not correct. In the 

 context it is stated that the columella is spongiose and well developed. 

 The part of the coral towards the left hand of the observer in the 

 plate (this was not reversed by the artist) shows most distinctly 

 that there are long wavy and geniculate septo-costa?. They are in 

 groups, as it were. The type specimen is in the Museum of the 

 Geological Society, and its faithful resemblance to the figure given 

 on plate xxii. of the monograph of Milne-Edwards and Jules Haime 

 of ' Corals from the Great Oolite,' is very remarkable. It is correct 

 in every respect except in the indiff'erent printing of the very 

 distinct columeUae, which are formed by the septal ends and also by 

 some additional tissue. The description of the species agrees with 

 the drawing and with the type. 



Mr. Tomes writes, p. 184, " All the specimens recently collected 

 at Combe Down may be referred either to Clausastrcea Pratti or to 

 Isastrcea Conyhearii, according to the condition of the specimen 

 examined. 



In disputes of this kind we must take the type specimen for the 

 jjurpose of comparison ; and then it is perfectly evident that the 

 two species mentioned above, and which were described and figured 

 by Milne-Edwards and Jules Haime, are generically distinct. The 

 long and often geniculate costse which unite the septa of somewhat 

 distant calicos in one species are totally opposed to the diagnosis 

 of an Isastrsean. Isastrcea Conyhearii has, from the description and 

 figure, all the characters of an Isastrsean, and such septo-costae as 

 exist in the other form could not by any possibility be produced 

 by weathering. 



There is merely a slight union of a thinning-out septum in the 

 axial space of the Isastraean with one or more of its fellows ; but in 

 the type of the other species there is thickening of the septal ends, 

 and the axial space is as it is in recent corals which have columellae 

 made up by the inner ends of the septa, more or less additional 

 tissue being added. Such a columella is a parietal one, and when 

 well preserved in recent and fossil forms often exhibits papillae at 

 the free surface. 



It is to be noticed that Mr. Tomes persists in placing the species 

 of coral with a columella and geniculate and more or less grouped 

 septo-costae in the genus Clausastrcea, in spite of Milne-Edwards 

 and Jules Haime having removed it from that genus 28 years since. 

 They placed the form as a sjDecies of Plerastrcea. Ho writes 

 (p. 183) : — " Under the impression that the so-called Clausastrcea 

 Pratti has an essential columella, the original describers transferred 

 it to the genus Plerastrcea, in which genus it appears in their general 

 work on corals. 



