120 (Jincinno.U Society of Natural History. 



usually raised into monticules that ma}^ be composed either of densely 

 cellulose tissue, or of slightly larger or smaller tubes than those of the 

 average size. 



Type: A. hirsuta. 



From the forms usually classed under Monticulipora, species of this 

 genus are principally distinguished by the pseudo-septa, which are 

 developed onl}^ at rare intervals in some of the species of that genus. 

 Of the described species, Ghoitetes ortoni. Nicholson, is the only one 

 known to me to possess the characters of Atactopora. All the other 

 species referred to the genus, I believe to be new to science, and I 

 have so described them. 



Atactopora hirsuta, n. sp. (Plate XII., figs. 3, 3a, 36.) 



[Ety. — Tlirsutus, rough, spinous.] 



Bryozoary growing parasitically attached upon foreign objects (usual- 

 ly coating an Endoceras), and forming ver}^ thin, sometimes much ex- 

 panded crusts, not more than one half a line, and genei'ally less than 

 one fourth or one sixth of a line in thickness. Surface set Avith nu- 

 merous, rounded or slightly elongated tubercles, having no distinct ar- 

 rangement, and placed at distances apart of one line, more or less. 

 Tubercles compact at their summits, the continuity of the compact 

 portion frequently disturbed by the interpolation of calices of the or- 

 dinary size; the structure of the summits is minutely porous, though 

 the pores usually can not be distinguished at the surface, and nearly 

 the entire mass (of the tubercle) appears to be solid. Tubes some- 

 what oblique to the surface in very young specimens, and direct 

 in older examples, thick-walled, nearly equal in size, apparentlv with- 

 out any very minute interstitial tubuli. Tube calices small, elliptical 

 to sub-rhomboidal, ten to twelve in the space of one line, their margins 

 thick, and carrying two rows of minute tubercles, that are almost in 

 contact and project over and into tube orifices, and are probably con- 

 tinuous with the small pseudo-septal ridges on the inner surface of the 

 tubes. 



Transverse sections prove the existence of the pseudo-septal ridges 

 just mentioned. They are small, and number from three to four in 

 each tube. 



Atactopora ortoni, Nicholson, in man^^ respects resembles this 

 species, but the two can be readily distinguished by the difllereuces 

 existing in the surface tuberosities. In Prof. Nicholson's species the 

 monticules are conical, smaller, more closely set, and are regularly ar- 



