24fi REPORT ON ALBATROSS MOLLUSC A DALL. 



of lateral plications, arising in connection with the fossette of the car- 

 tilage from the true cardinal teeth ; in the influence of the environment 

 ou the degeneration of hinge characters ; in the estimate of the charac- 

 ters of the primitive bivalves, and some minor points, we had arrived 

 independently at the same conclusions, and even illustrated them by- 

 identical or nearly identical examples., This is certainly strong pre- 

 sumptive evidence of the correctness of those inferences. In the points 

 in which we differ it seems to me that the differences arise from the 

 fact that Neumayr has approached the subject more from the paleonto- 

 logical stand-point, and has less considered or has given less weight to 

 biological considerations, not imprinted on the shell; while in my own 

 case, from the nature of my previous studies, I have been led to attack 

 the problem from the other side. Eecent investigations, available only 

 since the date of Neumayr's paper, have thrown much light on the in- 

 osculation of characters not before known to interlace. Neumayr,also, 

 from my stand-point, has insufficiently grasped the importance of the 

 different processes involved in the production of the internal cartilage 

 and its shelly coefficients on the one hand and the denticulation of the 

 hinge margin on the other. These two processes, though they must often 

 have proceeded simultaneously in the same genus, were not necessarily 

 connected, except in so far as by resulting stresses each might react on 

 the hinge-product of the other. So instead of having a Desmodont type 

 of hinge as opposed to a Priouodont, and, as Neumayr would say, a 

 Heterodont (Teleodont) type, we may have either an Anodont (Paleo- 

 conch), a Prionodont (Taxodout), or a Teleodont (Heterodont) type of 

 hinge, either with or without an internal cartilage and its accessories. 



By the elaboration of this view, as attempted in the foregoing discus- 

 sion, it seems to me the discrepancies so evident in Neumayr's system 

 have been avoided, the types of hinges assigned their proper weight in 

 the system, while those biological relations which are not fully reflected 

 in the shelly parts have not been slighted ; though inevitably numer- 

 ous improvements in detail will suggest themselves to students, or be 

 effected by a future expansion of our knowledge. 



As regards the Eudistes, if, as claimed by Woodward and others, 

 they possessed an internal cartilage, it is probable that they must form 

 a specially modified and extraordinary ramification of the Chamaeea. 

 If, however, as is claimed by some authors, there was no internal carti- 

 lage or external ligament, no hinge, properly speaking, and the smaller 

 valve simply rose and fell vertically under the control of adductor mus- 

 cles, guided by interlocking processes, it is evident that this would es- 

 tablish an inter-relation between the valves, unlike anything among the 

 Pelecypods, and only comparable, perhaps, with that of certaiu oper- 

 culated corals. In the latter case the Eudistes would have to be re- 

 garded as ranking at least among the subclasses, if as Mollusca at all. 

 My own impressions are that the first-mentioned view is the more prob- 

 ably correct one. 



