194 HYATT, 



As will be seen in the descriptions of the species, al- 

 though the same varieties occur in different localities, and 

 under diverse physical conditions, still the specimens 

 even of different species in each locality usually have a 

 similar character. The adhesion of the branches is owing 

 entirely to the juxtaposition of young cells, whose softer 

 ectocysts adhere to one another, and it is therefore a char- 

 acteristic which may occur in any species when the young 

 cells are accidentally brought in contact. 



Tubular. All the Fredericellse have tubular branches, 

 the zooids being arranged in a single series. 



In Plumatella Arethusa the tubular characteristic is re- 

 tained even in variety b. In variety b of P. diffusa, how- 

 ever, the branches coalesce to a considerable extent ; and 

 in varieties b and c of P. vitrea, either single branches 

 or whole colonies may have the polypides in bunches, ap- 

 proximating to the mode of growth exhibited by Pectina- 

 tella. The branches of Lophopus are true lobes contain- 

 ing a fascicle of polypides at the end of each branch, and 

 those of Pectinatella are also lobes, but with the poly- 

 pides placed in long, double rows on the upper sides. 

 This lobation, therefore, arises as a characteristic of the 

 varieties or even as a peculiarity of one branch of a col- 

 ony, as in P. vesicularis,* and becomes of generic value 

 in Lophopus, Pectinatella, and Cristatella, entirely super- 

 seding the tubular form of the branches in Fredericella, 

 P. Arethusa, and the varieties of the remaining American 

 species. 



CXENCECIAL CELLS. 



Distinct. In Fredericella the cells are distinct from 

 each other ; occasionally by some accident, as previously 

 mentioned, a branch may become adherent to a neigh- 

 boring branch, but the cells never appear to do so. The 

 cells of the Plumatellse are adherent in all their Alcyonel- 

 loid varieties. 



Cell-walls entire. Wherever the cells are distinct, the 

 cell-walls must be entire. When, however, the former be 



* See description of species. 



