SUB-GENUS HETEROTRYPA. 115 



of the walls of the corallites is also the same, and both show 

 exactly corresponding features in longitudinal sections (fig. 

 19, b). Upon the whole, therefore, there can be no hesitation 

 in concluding that the mere external difference in the form of 

 the monticules, being unaccompanied by any features of inter- 

 nal or structural difference, ought not to be allowed to count 

 as of more than varietal value. 



Var. 11. — M. ramosa, D'Oib., var. Dalii, E. and H. 



(Fig. 19, c and d; and PI. II. fig. 4.) 



Obs. — Not having had the opportunity of examining the 

 original specimens upon which Milne-Edwards and Halme 

 founded their Chcetetcs Dalii (Pol. Foss., p. 266, PI. XIX. 

 figs. 6, 6a, 1 851), I cannot be absolutely certain that I have 

 correctly identified it. Judging, however, from their figures 

 and descriptions, I have little doubt that the form which I 

 described as Chcstetes appTOxiviatiis (Quart. Jour, Geol. Soc, 

 vol. XXX. p. 502, PI. XXIX. figs. 3, 3c7, 1874) is really the 

 same. Accepting this conclusion, the differences and resem- 

 blances between ]\L raviosa, D'Orb., and J\l. Dalii, E. and H., 

 may be briefly stated as follows : As regards external charac- 

 ters, M. Dalii precisely agrees with the type-form of AI. 7'anwsa, 

 D'Orb., except that the monticules are much reduced in size, 

 and that the Interstitial tubuli are sometimes not quite so con- 

 spicuous or numerous. The monticules (PI. II. fig. 4) are no 

 longer boldly prominent or conical, but are much smaller, and 

 in general either gently rounded or somewhat elongated trans- 

 versely. With the above slight external difference, there is 

 associated a complete agreement In Internal structure, both 

 tangential and longitudinal sections (fig. 19, c and d) showing 

 features precisely similar to those exhibited by corresponding 

 sections of typical examples of ]\L ramosa, D'Orb. I cannot 

 doubt, therefore, that as In the case of the so-called AT. I'uq-osa, 



