548 -P^'o/! 0. C. Marsh — The Value of Ti/pe-Sjjecimens. 



e. "Wax squeeze of the same ; showing pores and flooring-plates of the groove 



as they would appear on the inside of the test. 

 /. Similar squeeze from a part of the groove nearer the periphery, showing 



the twisting over of the flooring-plates. 

 Fig. 3 (E 7,583). Actinal surface ; the crack running from N.E. to S."\V. shows the 



fracture that enabled the transverse section, Diagram 2, to be reconstructed. 

 Fig. 4 (E7,o84). Abactinal sm-face ; shows imbrication of peripheral area, and 



traces of the frame. 

 Fig. 5 (E 7,685). Actinal surface ; the pentagonal area at the actinal pole is well 



marked, owing to the breaking away of the portion of the cast that 



represented the covering -plates. 

 Fig. 6 (E 7,586). «. Actinal surface. 



h. Abactinal surface ; shows large central hollow and traces of frame. 

 Fig. 7 (E 7,587). a. Actinal surface ; the line x — y is that of the section h ; this 



latter shows the trace of the frame in the left half. 



c. Portion of abactinal surface of specimen, showing marked trace of the frame. 



d. Wax squeeze from impression of same in matrix, therefore representing 



outside of test ; shows imbricating plates more distinctly, but trace of 

 frame far less distinctly. 



V. — The Value of Type-Specimens and Importance of thkir 

 Preservation.^ 



By Professor 0. C, Marsh, M.A., Ph.D., LL.D., F.G.S.; 

 of Yale College, New Haven, U.S.A. 



IN the present state of Natural Science, there are too many 

 obstacles in the path of the original investigator. That this is 

 the case in the study of Botany, we may well believe, as authorities 

 of that science have frequently placed the fact on record. It is 

 certainly true that everyone who does original work in systematic 

 Zoology, either among the living or extinct forms, meets many 

 difficulties at the start in endeavouring to ascertain what others 

 have done before him. The literature of the subject is often dis- 

 couraging from its extent, and especially from its uncertainty. If 

 the work in hand requires the comparison of type-specimens, the 

 diflSculties greatly increase, and often prevent definite conclusions. 

 The type will frequently be found the most important element in 

 the problem, far more so than the literature, however extensive. 

 This is more especially true among the extinct vertebrates, with 

 which the present communication mainly deals. 



1. The Valve of Type- Specimens. 



The value of a tj^pe depends first of all upon whether it is 

 a characteristic specimen, worthy of being the representative of 

 a new group of individuals. Without this distinctive quality, its 

 importance is greatly diminished. If, for example, the specimen 

 first described, is immature, its essential features may thus be 

 obscured, and its value as a type much diminished. On the other 

 hand, a very old animal may be uncharacteristic. The teeth of 

 a mammal, for instance, may be worn down or even lost, so as to 

 make the normal dentition uncertain. This is true of recent forms, 

 but is more important if the type belongs to an extinct fauna, as 

 then the chance of duplicating it is much less. 



1 Read before Section B, International Congress of Zoology, Cambridge, England^ 

 August 23, 1898. ' 



