i6o Cincintiati Society of Natural History. 



regard them as of little reliability.* We have in the first part of 

 this article quoted several passages, showing that the internal struc- 

 ture of the specimen is not a character to be relied upon. It is a 

 fact that in all the descriptions of species the form, and external 

 features generally, of the corallum, are specially described. In- 

 deed in many cases these external features are the very ones which 

 serve to distinguish species. Not only species, but sub-genera, 

 also. For example in Constelt-aria, the star shaped monticule 

 is the main distinguishing mark. In Dekavia it is the conspicuous 

 blunt spine like processes. In Fistulipora it is the presence of 

 interstitial cells which completely isolate the larger tubes. All 

 these are external features. Again in Callopora we read: " . . the 

 species of Callopora are remarkably persistent in their internal 

 structure, and the points mainly to be relied upon in distinguishing 

 the species are external. "f Again in speaking of the separation of 

 two new species the same writer says: "As the differences in in- 

 ternal structure are so slight, the external characters, such as the 

 form of the zoarium (corallum) and monticules, must mainly be 

 relied upon in distinguishing the two species."]; 



Similar extracts could be made from Dr. Nicliolson, but these, 

 with those previously quoted must suffice. 



With these facts in mind, we have decided to make the exter- 

 nal features the basis of our classification, beginning with the general 

 form of the corallum, and dividing each section according to other 

 external features. 



Group I. — Massive : Free, or attached at one point or by the 

 whole of the base: more or less spheroidal, globose or massive. 



a. Surface smooth; corallum massive i. 

 Corallum free, spheroidal, 2. 



h. Surface not smooth; massive, with monticules, 3. 

 Spheroidal, nodulated, 4. 



*There can be no doubt but that such diverse forms as M. 7nammulaia, M. gracilis^ 

 M. o^tiealh, and many others resemble each other closely in their internal htructure. 

 The same may be said of M. 7vintcti .quixdrala^clavacoidea, pavonia^pulcliella^ calceola, 

 bri'area, tuberculala and others, in all of wliich great similarity of structure is found 

 This being the case it might be argued with good grounds that differences of interna 

 structure are more of the character of individual variation than much more. And i 

 this be the case, then the highly magnified sections of the inteiiur are valueless for jiur 

 poses of identitication. A good figure of the natural size sliowing the external features, 

 and another showing the appearance of the surface as seen under a good magnifier, 

 would be of more value for purposes of identitication, than any number of magnified 

 figures of the interior One of us has made sections of dendroid species, which are so 

 nearly identical in internal structure with discoid and conical species, as to make it a 

 matter of great difficulty to see any difference between them. 



With the evidence then, as presented in this paper, we believe that the external 

 form and markings of the group of organismsunder consideration are much more reliable 

 for the determination of species than the internal structure. At any rate the plan here 

 adopted is a practicable one, while the other is very impracticable, if not impossible, and 

 is not to be relied upon to any great extent. 



+Ulrich in 14th Ann. Kept. Geol. and N. H. Sur. of Minn., p. 96, 1SS6. 



]:lbid,p.87. 



