210 



HYATT. 



nate motion; their interior divided by walls of reticulating 

 muscular fibres into numerous radiating cells and tubes. 

 The latter, however, do not meet internally, but leave a 

 vacant space in the centre of the ccencecial trunk unoccu- 

 pied either bv the polvpides, or the muscular walls (PL 13, 

 figs. 2, 3, A'j. 



The polypides extend to the full length of their evagina- 

 ble endocyst, and are destitute of an invaginated fold, not 

 even possessing a fillet around the upper edge of the cce- 

 ncecial orifice as in Pectinatella (PI. 14, fig. 1). They are 

 disposed in rows upon the borders, inclosing the clear, 

 bare central spaces with an edging not unlike the polypid- 

 al fringes of Pectinatella (PI. 13, fig. 1). 



The ectocyst loses the fixed character it still possessed 

 in Pectinatella, and is only a transient, gelatinous excre- 

 tion, thrown off in great abundance from the common base 

 of the colony (PI. 1-3, fig. 3, D). 



The communities are not invariably gathered upon a 

 common ectocyst, as in Pectinatella, but are sometimes 

 single, as in Lophopus. 



There is, however, a very curious, and remarkable simi- 

 larity of one species with Pectinatella. 



The ccencecia of C. opbidioidea herd together within 

 confined boundaries from a few inches to a foot or more 

 in diameter, covering such favorite resorts with a glairy 

 coating accumulated upon the surface by the moving 

 bases of the numerous colonies. The aspect of one of 

 these settlements, supported upon this common ectocyst, 

 is analogous to that of a mass of Pectinatellae ; especially 

 to the old age, or degradational period of the life of a mass 

 of the latter ; where a large number of colonies still cling 

 to a thin sheet of gelatine left from the decay of the great- 

 er part of the ectocyst. 



This similarity may be explained by the fissiparous 

 multiplication of the ccencecia in both genera and the slow 

 progression of Cristatella. The colonies of the last can 

 never wander far from their place of origin, unless floated off 

 by some accident, and, continually multiplying, they soon 

 create a dense population in a comparatively small space. 



The distribution of Cristatella is similar to that of Pec- 

 tinatella, thev being generally found together. 



