ORDER IV CRYPTOSTOMATA 339 



large, prismatic, witli horizontal diaphragms. Mesopores few to numerous, varying 

 in size. Ordovician and Silurian. 



Monotrypa Nich. (Ptychonema Hall) (Fig. 495). Distin- 

 guished from the preceding by the absence of mesopores and 

 fewer diaphragms. Ordovician to Devonian. 



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

 fora Dybowski (Fig. 496). Ordovician. 



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

 dovician and Silurian. Fig. 496. 



Dittopora colliculata 



Eieliw. Ordovician ; Es- 



Order 4. CRYPTOSTOMATA Vine. thonia. Tangential .sections 



with two sets of acantlio- 



Primitive zocecium short, pyriform to ohlong, quadrate or P°"^''' 'i ^■^ 

 hexagonal, sometimes tubular, the aperture anterior. In the 



mature colony the aperture is concealed, occurring at the bottom of a tubular shaft 

 {^^ vestibule"), which may be intersected by straight diaphragms or hemisepta, owing 

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

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

 supia and avicularia wanting. 



The Cryptostomata differ from the Trej)ostomata chiefly in that the " immature " 

 region (primitive cell) is usually much shorter 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 tlie ramose 

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

 presence of hemisepta, similar to those occurring in the vestibule of Escharopora and 

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

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

 Ooeloconus, Rhombopora, 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 zooecia 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 

 Escharopora.^ 



The Cryptostomata are probably nothing more than Paleozoic Cheilostomata, 

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

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

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

 l^olypides 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 tubular prolongation of the aperture. Thus, the Recent 

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

 are never found in the Cyclostomata and Trepostomata, bitt 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 beeu to accept the presence of tubular zooecia as fully 

 demonstrating the Cyclostomatous affinities of the species producing them. Investigations, how- 

 ever, show that the mere form of the zocecium cannot be relied upon as a subordinal character any 

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



