THE MOEPHOLOGY OF THE CHEILOSTOMATA. ?09 



mandible, and another distal to the same structure, and 

 common to it and the supra-avicularian compartment. From 

 various parts of the membrane covei-iug the dorsal fenestrtie 

 rise the spine-like processes to which the variety owes its 

 name. 



Catenicella hastata, Busk' (fig*. 55). 



The supra-avicularian compartment {sup. avic.) is calcified 

 except at its extreme tip, the walls being perforated b}' small 

 pores. It forms a broad, flattened spiue at the upper lateral 

 coruer of the zocEcium. Tlie avicularian mandible is minute, 

 but the avicularium possesses, in addition to its occlusor and 

 divaricator muscles, a polypide rudiment [pol.), as in various 

 other Cheilostomes. I have noticed a similar structure in other 

 species of Catenicella. The infra-avicularian compartment 

 {inf. avic.) is completely divided into two. The outer wall of 

 both these cavities is usually completely calcified, but the 

 proximal one may have a slit-like membranous fenestra, 

 which is usually lateral. Between the proximal portion, 

 designated by Waters (1883, p. 428) the "pedal compart- 

 ment," and the zooecium, was noticed a row of three com- 

 munication pores (^.p.)- A comparison with Vittaticella 

 suggests that the vitta3 shown in fig. 56 are the last remnins 

 of the pedal compartments with their communication pores. 

 This view has already been maintained by Waters (p. 428), 

 and, though not quite in the same manner, by Jullien (1888, 8). 

 I have no suggestion to make with regard to the function of 

 the lateral "compartments" in Catenicella. 



The frontal wall has from seven to nine small fenestrre, from 

 which tubular cavities pass transversely towards the middle 

 line. The arrangement is strikingly Cribrilina-like, and 

 the resemblance is intensified by the existence of irregular 

 slit-like cavities alternating with the fenestrre, which suggest 

 an incomplete lateral fusion of frontal bars. 



The compensation-sac is usually cleai-. Its floor aj)peai's to 

 be deeply pigmented, but this may be the result of the 

 ' Busk (1852), p. 7; 1884, p. 10. 



