62 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DcC. 20, 



extent to which they are capable of being paralleled ; and certainly 

 it seems as if the verdict were in favour of as near a relationship ex- 

 isting between the Isopoda and Trilobita as that which undoubtedly 

 does exist between the Xiphosura and the Eurypterida. 



Past progress in palseozoology has been so great, that I am 

 unwilling to conclude with Dr, Dohrn that many points in the 

 genealogy of the Crustacea will probably never be cleared up. 



What we seem to need most is, more ivorhers, not more fields for 

 palseontological research. 



Seldom has a more complete series of remains of any order been 

 met with in a fossil state than those of the Ptevygoti collected in 

 Lanarkshire ; yet these are but the work of one man, Mr. Robert 

 Slimon, of Lesmahagow, from the bed of one small stream, the 

 Logan Water. 



The same remark applies to the researches in the Trilobita, carried 

 on by M. Barrande, in Bohemia. 



If the Trilobita have already told us so much of their history, 

 may we not yet expect to learn more ? 



Surely if Mr. Billings's single specimen and that in the British 

 Museum really exhibit legs and a palpus, which ther6 seems no 

 reason to doubt, then others may certainly be looked for and found, 

 and that probably ere long, exhibiting more clearly what is the 

 true organization of this ancient family of the Crustacea. 



Dtscijssion. 



Prof. T. RtrpEET Jones remarked upon the high critical value of 

 the paper and on the interest attaching to the study of the Crus- 

 tacea, and called attention to the apparent absence of any indica- 

 tions of convergence in our present knowledge of the class. He 

 thought that we must nevertheless look back to some point of di- 

 vergence from which the varied forms known to us may have pro- 

 ceeded by evolution. 



Prof. Macdonald remarked that difficulties must be expected to 

 occur in classification. He believed that all Invertebrate animals 

 were to be regarded as turned upon their backs, as compared with 

 Vertebrata. The cephalic plate in Limulus he regarded as the 

 equivalent of the palate-bone. The incisive palate was very distinct 

 in the Crabs. The absence of one pair of antenuEe did not appear 

 to be any reason for removing Lhmdus from the Crustacea. 



Dr. MuRiE considered that the contemplation of the multitude of 

 young forms referred to by Mr. Woodward should serve as a warning 

 to describers of species, and also as a check to generalizations as to 

 the number of species occurring in various formations. He re- 

 marked that if we were at a point when the presence or absence of 

 a single pair of nerves could be taken as distinguishing class from 

 class, these classes must be regarded as very nearly allied. He 

 thought that the doctrine of evolution was being pushed further 

 than the known facts would warrant. 



Mr. Woodward, in replying, drew attention to the diagrams of 



