66 



BULLETIN 77, UNITED STATES NATIONAL MUSEUM. 



Fig. 11.— Coeynotrypa abrupta. a and 6, portions of 



THE TYPE-SPECIMEN, X9 AND X20, INCRUSTING A FRAG- 

 MENT OF Rhynchotrema capax. Richmond group, 

 Iron Ridge, Wisconsin. 



proximal stolonal portion is almost threadlike, being not more than 



0.04 mm. in width. Tliis diameter is retained until the anterior 



third or fourth is reached, when the zocscium abruptly swells, with 



an angle of divergence of 50°, and becomes rounded, with a diameter 



of 0.20 to 0.25 mm. An 

 average zooecium and its 

 stolon is 1.0 mm. long, but 

 in individual zooecia of the 

 same zoarium the threadhke 

 proximal portion may range 

 in length from less than 0.10 

 mm. to 1 mm. The swollen 

 anterior zooecial portion, 

 however, is fairly constant in 

 its measurements, as no devia- 

 tion from a width ranging be- 

 tween 0.20 mm. and 0.25 mm., 

 and a length of 0.32 mm. to 



0.40 mm. has been observed. The apertures are round, subterminal, 



bordered by a slightly elevated rim, and small, averaging only about 



0.09 mm. in diameter. 



Corynotrypa ahrupta is easily distinguished from all other species 



of the genus by the narrow stolon and the very abrupt swelling of the 



zooecium proper. In related species such as C. injiata (Hall) and C. 



delicatula (James), the angle of divergence is less, giving a different 



shape to the zooecium as a whole. The 



extreme variation in the length of 



the narrow proximal portion is noted 



above, and is indicative of the fact 



that this part of the zooecium is the 



least stable in simple species of 



Cyclostomata. 



Occurrence. — The American speci- 

 men illustrated in figure 11, upon 



which the species is based, incrusts a 



fragment of RTiyncJiotrema capax and 



was found in the liighest beds of the 



Maquoketa shale of the Richmond 



group, at Iron Ridge, Wisconsin. The 



Russian examples assigned to the 



species were found associated with Calapcecia cribriformis Nicholson, 



Halysites sp., Streptelasma, and other fossils of the coral bed, in the 



Lyckholm limestone (Fl), at Kertel, island of Dago. 



H olotype.— C&t. No. 54173, U.S.N.M.; Paratype, Csit. No. 57109, 



U.S.N.M. 



Fig. 12.— Coeynotrypa abeupta. o and 6, 

 portion of a zoarium, X9 and X20, in- 

 crusting A crinoid column. Eaely 

 Silurian, Lyckholm formation, Kertel, 

 island of Dago, Esthonia. 



