338 SIDNEY F. HARMKR. 



double '^ectocystj" that is, as forms in which there is a 

 calcareous cryptocyst internal to the frontal membrane. 

 Although Gregory was justified in regarding the Cribri- 

 linidae as forms in which the frontal membrane persists, 

 the view which I take of the compensation-sac involves 

 the conclusion that the membrane persists even in the 

 Eschariue genera. The Cribrilinidte may be regarded as a 

 transition-group between the Flustrine and the Escharine 

 forms; but, as I have pointed out above, it appears to me 

 that the family, as at present constituted, is not a natural 

 one. 



Although it is very difficult to draw a line between the 

 more simple species of Membranipora and those in which 

 a definite cryptocyst occurs, it is hardly possible to speak of 

 some of the former as diplodermatous. Although the term 

 Athyriata is antedated by Diplodermata, it is more in 

 accordance with the structure of recent genera than Jullien's 

 term, and in the present state of our knowledge it would 

 perhaps be well to accept it as the name of a group in- 

 cluding those forms in which the frontal membrane persists 

 in more or less its primitive form, whether a cryptocyst is 

 present or not below it. 



The Athyriata are thus, ou pahiDontological evidence, the 

 oldest group of Cheilostomes. In the Cretaceous period they 

 had already differentiated themselves into the types of 

 structure represented by Membranipora, Ony chocell.i, 

 and Micropora, in the latter two of which the cryptocyst is 

 well developed. The Cretaceous period is also characterised 

 by the occurrence of a number of s])ecies belonging to the 

 transitional Cribrilinid type. So far as the evidence goes 

 at present, the true Escharine forms were then much inferior 

 in number to the dominant Athyriate group. 



With regard to the other parts of Gregory's classification 

 (180P), p. 223), it appears to me that the sub-order Stolonata 

 includes several families of very different affinities, the 

 EucrateitUe at any rnte probably belonging to the Athyriata. 

 Some of the Cellulai-ina are also Athyi-iate, while I agree 



