124 



THE LESSER CHKLOMANS ETC. 



those species which seem to be most fully represented. Perhaps 

 the writer may have committed no great error in distributing to 

 each the fragments derived from it, but his attempted restora- 

 tions of carapaces and plastrons are as like as not inaccurate 

 representations of their natural form. But this risk was inevi- 

 table, since the relative proportions of the several constituent 

 pieces of a carapace or plastron are clearly not to be ascertained 

 from any number of fragments of all ages and kinds commingled. 

 If, however, these sketches enable anyone to assign his fossils 

 to their natural position in the shell, or test as it may be better 

 termed, one useful end will have been served by them. 



As the divisions of the tegumentary layer of the test by no 

 means correspond with those of the bony stratum beneath, it 

 would be well if zoologists who are concerned with the former 

 only and osteologists whose observations are extended to the 

 latter would devise and adhere to a distinctive terminology for 

 each superficies ; much confusion and contradiction would be 

 thereby avoided. The osteologist necessarily finds in the 

 Chelydidffi a "nuchal" plate, at least a plate constant in that 

 position which cannot be called other than nuchal ; the 

 zoologist may or may not find in a species of the family a 

 " nuchal" shield marked off on the surface of the integument; 

 if not, he must contradict his colleagxie, who, moreover, has to 

 include in his "nuchal" plate a part of each of the surrounding 

 shields of the zoologist to the dire misunderstanding of each 

 observer. So of every other part. The marginals of" the one 

 are not the marginals of the other. The zoologist sees verte- 

 brals which do not exist in the bone beneath ; the greater part 

 of the last " vertebral" has no more to do with vertebrae than 

 has the " nuchal," and so on. The present writer presumes to 

 complain of all this, but not to remedy it for others. At the 

 same time he does not think it unreasonable that, in the present 

 unsettled use of terms, he should, for the purposes of the follow- 

 ing descriptions, employ those which seem to him convenient, 

 rather than continue the use of ambiguities. In speaking of 

 the carapace he will therefore call the anterior plate "lophial" 

 instead of nuchal, the rib-plates " pleural" instead of costal, the 

 hindmost plate of the dorsum " pygal," the hindmost of the 

 periphery " uropygial" rather than pygal or caudal, the other 



