BY T. WHITELEGGE. 339 



of intercalary growth, as far as I have been able to ascertain, 

 are recorded by Mr. Hincks, but in these cases it is confined to 

 the ovicelligerous cells of Schizoporella hyalina, and S, linearis. 



The formation of new zooecia does not appear to be confined to 

 any particular part, but may take place at any point between the 

 centre and the margin ; when near the latter the zocecium is formed 

 in the space intervening between two, and when nearest to the 

 former in the intervening space bounded by four zooecia. The 

 direction of the zocecia is also apparently reversed, from the fact 

 that the free distal edge of the opercu^lum is nearest to and 

 directed towards the apex in those of a conical form, and to the 

 apparent base in those which are flattened ; while the hinged end 

 or proximal is nearest to the outer margin of the zoarium. 



The manner in which the peristomial orifice is formed appears 

 to be just the opposite to what obtains in other peristomiate 

 Polyzoa, and there is a special feature of an important character 

 which, if not new to the class is exceedingly rare, and so far I have 

 searched in vain for the record of a similar structural element. 



The first indication of the formation of a new zooecium appears 

 on the upper surface of the zoarium as an elevated or depressed 

 round spot bordered on one side by a thin layer of epitheca. At 

 this point the "semilunar slit with the concavity directed out- 

 wards " is formed, and by the gradual extension of this slit to a 

 circular form a piece of the calcareous lamina is cut out, the 

 resulting oi^ening being that of the peristome, and at a short distance 

 below the true oral aperture is seen to be also in a fully formed 

 condition. It is the rule to speak of the opercular-bearing aperture 

 as the primary, and of the peristomial as the secondary orifice ; 

 but in this case it appears doubtful which ought to rank as primary 

 or secondary. 



In a median line above the mouth close to or upon the margin 

 of the peristome there is a circular or subcircular pore usually 

 covered by a membrane. It is this pore, when in an imperfect or 

 broken state, that has been mistaken for the proximal sinus in the 

 lower lip of the oral aperture ; but the true oral sinus is much 

 wider, and at the opposite end of the mouth to that of the pore. 



