126 



and other Infusoria. The muscles which move the horseshoe-shaped 

 cartilage constitute two pairs, one superior, the occlusors, which are at- 

 tached by a slender tendon to the upper angle of the expanded base 

 of the horns of the crescentic cartilage, and the other, the inferior or 

 dilators, which are inserted beneath the inferior angle of the same 

 base. These muscles, like the retractors of the polype, are marked 

 with transverse striae. The expanded portion of the cell, besides these 

 special muscles of the aperture, contains other muscular fibres, in all 

 respects resembling those described by Dr. Farre, as conducing to the 

 extrusion of the polype in Bowerbankia, and which are also very dis- 

 tinct in the Notamia, but which in the present instance would seem 

 to have for their chief function, the drawing up or corrugation of the 

 membranous portion of the polype cell. These muscular fibres have 

 a distinct central nucleus or thicker portion, as is the case in the 

 analogous muscles in the other cases just cited. It will thus be seen 

 that, in the important particular of the aperture, the received state- 

 ment that it is " inferior subterminal, oval, and with plain margins," 

 is in every particular incorrect. It is on the contrary terminal, cres- 

 centic, and one half of its margin constituted of a movable horny lip, 

 the other half formed by the calcareous wall of the polype cell, resem- 

 bling in fact, the aperture in Gemellaria, Notamia, and others, in 

 which part of the wall of the cell near the aperture is filled up by a 

 flexible membrane, attached probably in all cases, though this has not 

 yet been shown, to a movable horny lip with appropriate muscles. 

 This Bryozoon, therefore, together with, at all events, Gemellaria lo- 

 ricata and Notamia bursaria, must be removed from the family 

 Eucratiadce of Dr. Johnston, or the characters of that family must be 

 modified, as respects the situation and construction of the aperture of 

 the cell. 



I would direct attention to an appearance not unfrequent in the 

 polype cells, as if they had been repaired after being broken. This 

 appearance is seen in figs. 5 and 6. 



