ORDER IV CRYPTOSTOMATA 339 



large, prismatic, witli horizontal diapliragms. Mesoporcs few to niiineroiis, varying 

 in size. Ordovician and Siliirian. 



Monotrypa Nicli. {Phjchonema Hall) (Fig. 495). Distin- 

 gaislied from tlie preceding by the absence of mesopores and 

 fewer diapliragms. Ordovician to Devonian. 



Anaphragma U. and B. Ordovician and Silurian. Ditto- 

 pora Dybowski (Fig. 496). Ordovician. 



Trematopora Hall (emend. Ulr.) ; Stromatotrypa Ulr. Or- 

 dovician and Silurian. Fig. 49(5. 



Dittopora colliculata 



^ , . ^.^^....^«™^^,^^.. _ . . Eichw. Ordovician ; Es- 



Order 4. CRYPTOSTOMATA Vine. thonia. Tangential sections 



with two sets of acantho- 



Primitive zooßcium short^ pyriform to oblong, quadrate or P^""*^^' /i ^^ ^^^' *^^ ^^^' 



hexagonal, sometimes tubulär, the aperture anterior. In the 



mature colony the aperture is concealed, occurring at the hottom of a tubulär shaft 



(" Vestibüle "), which may be intersected by straight diaphragms or hemisepta, owing 



to the direct super-imposition of layers of polypides. Vestibulär shaft surrounded by 



vesicular tissue, or by a solid calcareous deposit ; the external orifice rounded. Mar- 



supia and avicularia wanting. 



The Cryptostomata diifer from the Trepostomata chiefly in that the " immature " 

 region (primitive cell) is usually much sliorter and the passage to the mature region 

 more abrupt. 



Some of the Cryptostomata are ramose, and have long, thin-walled prismatic 

 tubes in the axial region, with or without diaphragms, precisely as in the ramose 

 Trepostomata and Cyclostomata ; but they are distinguished from the latter by the 

 presence of hemisepta, similar to those occurring in the vestibule of E schar opora and 

 Phaenopora, two of the most typical genera of the Cryptostomata. That these axial 

 tubes are not of primary importance is shown by individuals of such genera as 

 Goeloconus, Bhombopora, etc., in which a second layer of zooecia has grown over the 

 first. This is a rare condition, and is probably to be attributed to an accidental 

 Interruption of growth. But, where observable, it is to be noticed that the inner 

 extremities of the zocecia of the second layer are not drawn out into tubes like 

 those of the primary set, but are short, and in all essential respects like those of 

 E schar opora.^ 



The Cryptostomata are probably nothing more than Paleozoic Cheilostomata, 

 dlffering, however, from the typical members of the latter, (1) in having neither 

 marsupia nor avicularia ; (2) in the much greater deposit of calcareous matter upon 

 the front of the zooecia, thns producing the vestibule ; (3) in that successive layers of 

 polypides are often developed, one directly over the other, in a continuous tube ; and 

 (4) in that whenever a zoarium attains an uninterrupted width of more than 8 mm., 

 it exhibits Clusters of cells differing more or less, either in size or elevation, from the 

 average zooecia. The last two distinctions are suggestive of the Trepostomata ; and 

 the presence of a vestibule reminds us of certain Mesozoic and Recent Cheilostomata, 

 which have the same tubulär Prolongation of the aperture. Thus, the Recent 

 Adeonella atlantica Busk, has not only a vestibule, but hemisepta as weil Hemisepta 

 are never found in the Cyclostomata and Trepostomata, but are a very common 

 feature of the Cryptostomata. They occur at the bottom of the vestibule, and doubt- 

 less served as supports for the movable operculum. 



^ The almost universal practice has been to accept the presence of tubulär zooecia as fully 

 demonstrating the Cyclostoniatous affinities of the species producing tliem. luvestigations, how- 

 ever, show that the mere form of the zofficium cannot be relied upon as a subordinal cliai-acter any 

 more than is the presence of tabulae in a tubulär organism a certain indication of an Anthozoan. 



