BRYOZOA. 271 



Dekayella prtenuntia.] 



vary considerably both in number and size, with medium conditions about as in 

 fig. 43. Acanthopores comparatively small, the principal set comparing in number 

 with the zocccia about as one is to four ; small set very minute, not often preserved, 

 at any rate, only rarely distinguishable in sections. 



Mua. Reg. Nos. 6019, 6020, 8073, 8305. 



Var. SIMPLEX, n. var. 



PLATE XXIII, FIGS. 38-42. 



In this form the mesopores are reduced numerically to a minimum. Indeed, 

 they are not distinguishable externally, and only a very few are to be made out in 

 tangential sections. The zooecial apertures are polygonal and unusually regular in 

 their arrangement. The walls, too, get to be stronger than in any other form of the 

 genus, with perhaps one exception, while the acanthopores are, if not smaller, at any 

 rate less noticeable in thin sections. From an external examination merely speci- 

 mens of this species might be regarded, and with good reason, as belonging to the 

 Amplexoporidtt 1 . Certainly they would scarcely be suspected of being closely related 

 to Dekayella prcenuntia. But with the aid of thin sections, vertical ones especially, 

 the true affinities of the form become obvious at once. Excepting that mesopores 

 are practically wanting, there is little or no difference between vertical sections of 

 the typical form of the species and var. simplex. 



Mus. Reg. No. 8307. 



Var. N^EVIGERA, n. var. 



(Not Figured.) 



This form differs from the preceding in having thinner zooecial walls, and clus- 

 ters of from five to thirty mesopores at the center of the usual groups of large 

 zocecia. In the var. simplex the zoarium consists generally of but few branches, but 

 in the best examples of the present form they are numerous, strong and divide and 

 inosculate freely, the whole forming a mass over 70 mm. in diameter. 



Mus. Reg. Nos. 6018, 7669. 



Var. ECHINATA, n. var. 







PLATE XXIII. FIGS. 32-38, 



This variety grows in large compressed branches, that seem never to inosculate. 

 The clusters of large cells are moderately distinct, and frequently enclose small 

 aggregations of mesopores. In having very few mesopores their structure agrees 



