40 Eobert E. Coker. 



the relations of marginal scutes and plates and will be seen again in 

 embryos and young of Thalassochelys. 



V violates the principle of adjustment in the anterior region. 

 The second neural, exceptional in being in contact with three pairs 

 of costals, is incompletely divided, but the significance of the incom- 

 plete seam is not evident. (Newmann's Fig. 4.) 



VIII presents a very unexpected neural series ; but this specimen 

 was an embryo and we do not know how its co-ordination would 

 have stood the test of life, nor whether post-natal seams would have 

 appeared to alter the plan of adjustment. Several of the specimens 

 mentioned above evidently would have shown less conformity if they 

 had been obser\^ed in the embryo stage. (JSTewmann's Fig, 38.) 



Another of NeMauann's specimens is of particular interest (IX). 

 The carapace is perfectly symmetrical, but there are five pairs of 

 costals and no additional neurals. ISTS is in contact with three 

 pairs of costals (C2, C3 and C4). Here is, therefore, a case of 

 mal-adjustment. However, l^ewmann found that the fourth costals 

 were growing forward underneath the third, and he interprets this 

 as a stage in the suppression of the third ("sixth," in his termin- 

 ology). If this interpretation is correct, we have the mal-adjust- 

 ment in process of correction, not, as in other cases, by the partial 

 division of the neural, but by the renioval of the supernumerary 

 costal. I do not say, however, that the imperfection of adjustment 

 is the cause of the squeezing off. 



Hence the exceptions are chiefly partial exceptions, and, on the 

 whole, even these specimens favor much more than they o]>pose 

 the assumption that the proper adjushneni of neurals and costals is 

 of more vital importance than mere number of scutes. Of course, 

 it is to be expected that turtles will show abnormalities in adjust- 

 ment as well as in number of scutes; but observation of the relative 

 frequency and degree of deviation from the usual numerical rela- 

 tions, on the one hand, and from the usual adjustment, on the 

 other hand, may be a means of estimating the relative value of 

 adjustment as compared with numerical relations. Supernumerary 

 scutes occur comparatively frequently, while mal-adjustment is rare, 

 and may it not be of some significance tliat in turtles with imperfect 



