MARYLAND GEOLOGICAL SURVEY 405 



shape and elevated, are in contact, with four to six in each row and this 

 greater number in about 0.8 mm. The furrows between the rows of 

 apertures are often irregular, and where this is the case the rows them- 

 selves are not continuous. When the arrangement is normal the average 

 width of the furrows is a little less than that of the rows of apertures, 

 allowing about four of the latter to come within the space of 1.0 mm. 

 The growing margins of the expansions are occupied by numerous crowded 

 angular cells, decreasing in size toward the extreme edge. Zooecial walls 

 minutely porous. 



Young zoaria have the aspect of a short-celled Tuhulipora, but Ave 

 believe the pinnate arrangement of the zooecia shown in maturer examples 

 Ip a surer indication of the true affinities of the species. Compared with 

 other species of Idmonea we know of none having anything like a fiabel- 

 late zoarium, all being strictly ramose. 



Pergens' retains d'Orbigny's Reptotuhigera, 1852, for the adnate 

 section of the genus Idmonea as currently understood, but since Lamou- 

 roux's type of Idmonea {I. triquetra Lamx., 1821) is also the type of 

 Reptotuhigera, it seems to us d'Orbigny's name has absolutely no claim 

 to recognition. Besides the separation of Idmonea into two genera, the 

 one comprising adnate forms the other erect, seems to find no sufficient 

 justification in either nature or convenience. 



Occurrence. — St. Mary's Formation. Cove Point (on Pecten madi- 

 sonius). 



Collection. — Mars'land Geological Survey. 



Genus CRISINA d'Orhigny. 



It seems to us there should be no question of the desirability of this 

 generic or subgeneric division. It is certainly convenient and as natural 

 as the difficulties of a genetic classification of the Cyclostomata will 

 permit. As we see it, precisely the same kind of difference separates 

 Crisina from Idmonea as that which distinguishes Truncatula Hagenow 

 from Osculipora d'Orbigny, Plethopora Hag. from Cyrtopora Hag., 

 Unicytis d'Orb. from Frondipora Imperato, and Corymhosa Michelin 

 from Fasciculipora d'Orb. 



' Revision des Bryozoaires du Cretace figures par d'Orbigny, Bull. Soc. Belse de 

 Geol., 1890, p. 338-340. 



