BRYOZOA. 567 



whole of the fenestrated expansion is preserved, observe the 

 angle at which it diverges from the axial line; (4) the charac- 

 ters of the branches, fenestrules and zocecia, and their number 

 in a given space. The actual thickness of the shaft is available 

 only to a limited extent, while the direction of the volution is 

 only an individual peculiarity, both dextral and sinistral spirals 

 occurring in, perhaps, all the species. The zoarium was free, 

 and in some species at any rate, consisted of more than one 

 spiral axis. In every instance where two spirals were preserved 

 in connection the}' are turned in opposite directions. Two ex- 

 amples of this kind are represented on PI. LXIII, figs. 9b 

 and 14. The first shows on the left side how a new axis is 

 formed. The outer margin of the perforated frond is at first 

 slightly thickened, then gradually recurved upon its celluliferous 

 side until a complete volution has been made. The succeeding 

 volutions follow at regular intervals. The extreme constancy 

 with which these volutions take place in, for instance, A. coin- 

 munis and A. proutanus is remarkable, and seems to me a severe 

 rebuke for those palaeontologists who decry what they are 

 pleased to call a burdening of nomenclatnre by the foundation 

 of species upon trivial individual peculiarities. Who is to say 

 that these characters are trivial?* 



Had I more space and plates at my disposal I would have 

 described and illustrated the minute internal characters of the 

 axis which in a number of species are quite distinctive. Magni_ 

 fled views of the fenestrated expansion, of which I give full and 

 complete descriptions, would no doubt have materially aided 

 in the determination of the forms, but they had also to be dis- 

 pensed with. The following tabulated list of the species in 

 which the more important features of each are noted, will, I 

 hope, partially atone for the deficiencies. , 



* In the three years that have passed since writing the above, I have collected 

 nearly a thousand additional specimens of Archimedes, In this large number every 

 specie* here described, save A . perminimus, is represented, besides several species as 

 yet undescribed. The study of these specimens has been most gratifying to me, since 

 I was thereby afforded the very best demonstration of the specific validity of the char- 

 acTcrs upon which the species were founded. Nor did I experience even ordinary 

 difficulty in discriminating between the species. 



