278 



MOLLUSCOIDEA BRYOZOA 



SUB-KINGDOM v 



Family 7. Amplexoporidae. Ulrich. 



Zoaria ramose, encrusting, discoidal, or 'massive, rarely bifoliate. Zocecial tubes com- 

 paratively simple, prismatic, with a well-marked divisional line between adjoining tubes. 

 Mesopores practically absent, but small abortive cells sometimes found among the large 

 zoozcia forming the monticules. Acanthopores generally abundant, sometimes wanting. 

 Ordovician to Devonian. 



Amplexopora, Ulrich. Zoaria ramose. Acanthopores always present, varying 



in size and number. Diaphragms 

 complete, horizontal. Ordovician to 

 Devonian. 



Monotrypella, Ulrich. Like the 

 above, but without acanthopores. Ordo- 

 vician to Devonian. 



Petalotrypa, Leptotrypa, and Discotrypa, 

 Ulrich. Ordovician to Devonian. 



Atactopora, Ulrich (Fig. 466). Zoaria 

 thin, growing on Orthoceras. Zooscial 

 apertures indented or floriform, accord- 

 ing to position of the very numerous acanthopores. Rather large, solid elevations, 

 composed of abortive cells, and completely filled by calcareous deposit, stud the surface 

 at regular intervals. Diaphragms thin, few, sometimes wanting. Ordovician. 



FIG. 466. 

 Atactopora maculata, Ulr. Cincinnati, O. Transverse 



Sub-Order C. CEYPTOSTOMATA. Vine. 



Primitive zocecium short, pyriform to oblong, quadrate, or hexagonal, sometimes tubular, 

 the aperture anterior. In the m,ature 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 superimposition of layers of polypides. Vestibular shaft 

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

 and avicularia wanting. 



The Cryptostomata differ from the Trepostomata 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 the ramose Trepostomata and Cyclo- 

 stomata ; 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 typical genera 

 of the Cryptostomata. That these axial tubes are not of primary importance is shown by such 

 genera as Coelocomis, fihombopora, etc., in whose axial tubes 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. 1 



The Cryptostomata are probably nothing more than Palaeozoic Chilostomata, differing, 

 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 zocecia, thus 

 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 



1 [The almost universal practice lias been to accept the presence of tubular zocecia as fully 

 demonstrating the Cyclostomatous affinities of the species producing them. Recent investigations, 

 however, show that the mere form of the zorecium 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.] 



