Genera of the ^outk American Palaeozoic Bryozoa. 



439 



quired for the accommodation of the polypide, and a growing 

 specialization of the mandible and its adjuncts. To a great ex- 

 tent the avicularium has lost its apparent status as a distinct 

 zooid in the colony, and become an appendage of the zooBcmm. 

 The bosses or mounds, so often forming part of it and supporting 

 the mandibular apparatus, are to be regarded as the homologue 

 of the chamber in the normal zooecium. Such forms as I have 

 now described, and others allied to them, may be classed as sec- 

 ondary or transitional avicularia. We must not suppose, how- 

 ever, that they constitute a clearly defined section ; they are con- 

 nected at all points by intermediate forms with the primary 

 group. Nor are these divisions coincident with any particular 

 genera or families ; the various modifications of the avicularia 

 are distributed sporadically over the whole suborder, with the 

 exception of the highest, which occur only in very narrow and 



definite limits. 



"The raised or pedunculate character commonly assumed by 

 the hollow portion of the avicularium in this division becomes 

 very pronounced in certain cases. The beak and mandible are 

 elevated on a distinct stem, and (we may suppose) obtain in this 

 way peculiar advantages for the discharge of their function, 

 whatever ?t may be. In such forms we recognize an advance 

 toward the peduncle of the true ' bird's head.' A nearer approach 

 to it is met with in the remarkable pedunculate avicularia which 

 occur in oae or two species of MembralNipora. The want of 

 mobility is perhaps the most essential distinction between this 

 form and the aviculariam of BuGUbA ; the beak and mandible 

 are less highly organized than in the latter, but the general char- 

 acter is the same in both, and very slight changes would serve 

 to convert the one into the other. 



" In Scrdpocellaria the avicularium is attached to the side of 

 the zooecium by its entire length, but ic is truly pedunculate, and 

 if attached only by the base, would bear a close general resem- 

 blance to the Bagulan form. 



" The mandible is curved in toward the extremity, and the 

 beak is somewhat hooked, so that the appendage has considerable 

 prehensile power. The chamber is not more than suificient for 

 the lodgment of the muscular fascicles. A still nearer approach 

 to the higher avicularium occurs in the remarkable form de- 



