^^^ Report of the State Geologist. 



scribed by Smitt under the name of Membranipora minax. 

 Here we have the perfect form of the ' bird's head ' (a curious antici- 

 pation of the organ as it exists in Bugula Murryana\ but there 

 is no basal joint and the whole structure is calcareous. A con- 

 nection is very clearly established between the simply mammillated 

 avicularium and the articulated through such forms as we have 

 in the true Membranipora minax, in Scrupocellaria ferox and in 

 the present species. 



"- In NoTAMiA we have probably the fixed form, which comes, 

 on the whole, nearest to the movable 'bird's head,' and consti- 

 tutes the most direct link between the two classes of avicularium. 

 Here the hollow portion (or chamber) is borne on a slender stem 

 of considerable length, from which it is separated by a partition; 

 it expands from the base upwards, and on the upper surface is 

 placed the curved beak ('like that of a cuttle fish'), occupying 

 about two-thirds of its length, at the base of which the mandible 

 takes its origin. The latter is much curved and terminates above 

 it in a sharp point. The upper edge of. the chamber below the 

 mandible surrounds a semicircular space, closed in by a mem- 

 brane, which probably represents the aperture of the normal 

 zooecium. Two new features (both of them present in the 'bird's 

 head') make their appearance in this form. The beak and the 

 portion of the chamber from which it arises are both of a horny 

 material ; in the lower form they are calcareous. Between the 

 mandible and the beak, when the former is elevated, a tuft of 

 minute set^, placed on a slight rising, is visible, which consti- 

 tutes a tactile organ, and conveys the external stimuli which 

 brings the muscles into play. It is possible that this structure 

 may exist in species in which it has not yet been observed, but 

 so far, I believe, it has only been noticed among the higher 

 forms, which I shall call the articulated avicularia, and in No- 

 TAMiA. In all but the fixed condition JSTotamia agrees with the 

 articulated group. It may, I think, be concluded that it is the 

 concomitant of the more highly specialized form . 



"I may add that the avicularia in the Notamia have very 

 much the shape and general appearance of zooecia reduced in 

 size, and are placed, like the latter, in opposite pairs. We pass 

 now to the articulated forms in which the zocecial type is com- 

 pletely masked, its elements being so modified as to constitute 



