502 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



Altogether it is believed that the club-shaped zooecia produced by 

 the constriction of the proximal end, and the small, neatly constricted 

 aperture with low peristomes, constitute sufficient characters to 

 justify a new genus, although it is recognized that several interme- 

 diate forms exist between this genus and Stomatopora, as here 

 restricted. 



This new cyclostomatous genus, in its method of growth and 

 general shape of the zooecia is quite similar to genera of other orders, 

 an occurrence which is not unusual in the Bryozoa. Such species as 

 Corynotrypa nitida or C. tenuichorda are exceedingly like elongate, 

 delicate forms of Hippothoa, and might readily be confused. The lat- 

 ter genus, however, a representative of the Chilostomata, has a sinus 

 in the lower margin of the aperture and an occasional well-marked 

 ooecium, as well as a very delicate surface ornamentation quite dif- 

 ferent, on close examination, from the simple punctate structure of 

 Corynotrypa. Among the Ctenostomata such genera as the recent 

 Arachnidium and the fossil Rhopalonaria are so similar in general 

 shape to Corynotrypa that at least one species of the last genus was 

 originally referred to the second. 



GEOLOGIC DISTRIBUTION. 



The geographic distribution of Corynotrypa has been briefly indi- 

 cated in previous remarks, and is also shown in the description of the 

 species. Regarding its geologic range, it is interesting to note that 

 the two typical sections of the genus show a somewhat parallel spe- 

 cific development. Thus, in the Ordovician, the most abundant, C. 

 delicatula, with a long geologic range, is accompanied through a con- 

 siderable part of this time by the equally abundant C. inflata. Dur- 

 ing earliest Silurian, when the deposits of the Richmond group were 

 being laid down, conditions seem to have been favorable for the 

 development or introduction of new, somewhat bizarre species, which 

 apparently did not survive for any great length of time. Among these 

 are the unusually large, swollen form, C. turgida, another equally well 

 marked species, C. curta, differing, however, in being exceptionally 

 small and short, and, lastly, C. ahrupta, with a long, slender stolon 

 and short, greatly swollen zocecium. 



In the Silurian, succeeding Richmond time, no representative of 

 the C. inflata section has been discovered so far, but the Devonian 

 contains a delicate species of each section. The next known occur- 

 rence of the genus is in the Mesozoic, where, as shown in the table on 

 page 504, again a single species of each section appears. The appar- 

 ent absence of the genus in the known Mississippian, Pennsylvanian, 

 and Permian rocks may be due to lack of systematic search, but it is 

 nevertheless a curious fact that all of the simple cyclostomatous 



