24 



of time the closure-plate is perforated by a fissure-like opening seated in its prox- 

 imal and median part (fig. 7). 



The Regeneration. In a few cases I have found zooecia regenerated in old ones 

 and more freqvent a regeneration of the heterozooecia, sometimes by a new hetero- 

 ozooecium sometimes by a zooecium (figs. 5, 7). Sometimes the new heterozooecium 

 may fill out the whole aperture of the old one (fig. 20), but if that is not the case 

 the space between the old and the new aperture is gradually closed by a calcareous 

 lamina which however is not formed as a unity, but as more (as a rule three) 

 plates filling out the spaces between as many calcareous processes. Fig. 9 shows 

 the three calcareous processes, and in fig. 5, which presents a zooecium regenerated 

 in a heterozooecium is seen a similar case in which the spaces between the three 

 processes have been filled out. In fig. 7 is seen a more irregular case and in the 

 case presented in fig. 22 the filling out of the narrow space between the old and 

 the new aperture has been prepared by the formation of short connecting processes. 



The Colonies are free with cylindrical branches, and in time increase in thick- 

 ness by the formation of superficial layers several of which may be seen at the 

 same time in different parts of the branch. 



This species is subject to a very great variation in all respects, and I have tried 

 in vain to divide the material examined in more different forms. We may discern 

 between the following two chief-varieties which are however very far from being 

 sharply limited. 



Var. latirostris. The subopercular area is longer than or as long as the aper- 

 ture, longer than broad; the oral ledge is narrow, and its height in the distal part 

 does not attain a third part of the height of the aperture. The marginal ridges are 

 narrow and the tubercles are small. The distal half of the heterozooecial aperture 

 is broad. 



Var angustirostris. The subopercular area is shorter than the aperture broader 

 than long. The oral ledge is broad and its height in the distal part attains the third 

 part of the height of the aperture. The marginal ridges and the tubercles are strongly 

 developed. 



I have examined colonies from Villedieu, Fecamp, Couture, Vendôme, St. Pa- 

 terne, Evreux and from Chatham. 



MeliceiMtites semiluna dOrbigny. 



Nodelea semiluna d'Orbigny, Bryoz. crét. p. 611, pi. 735, figs. 9— 11, 

 — — Gregory, Cret. Bryozoa p. 307. 



(PI. VI, figs. 4—6.) 



The Zooecia which have a more or less distinct rhombic or hexagonal outline 

 and the subopercular area of which is as a rule convex or flat, and more or less 

 distinctly ascending towards the aperture are rarely divided by indistinct marginal 

 ridges, and as a rule there are no tubercles. The aperture which is about as long 



