142 



BULLETIN" n, UNITED STATES NATIONAL MUSEUM. 





correctly, that liis specimens were derived from the Wesenberg lime- 

 stone. Pachydictya elegans, a species corresponding to his figures of 

 M. cyclostomoides in some respects, is present in the Wesenberg lime- 

 stone, and it is possible that Eichwald had this species before him. 

 However, in view of the imcertainty of accurate identification, I have 



decided to adopt Eichwald's name, not 

 to replace the American P. elegans, 

 but for a common bryozoan in the 

 Kuckers shale and higher formations, 

 differing mainly in having larger zoce- 

 cia, a less ornamented surface, and a 

 broader zoarium. If Eichwald's fig- 

 ures can be relied upon, he probably 

 illustrated this large-celled species. 



Pachydictya cyclostomoides, as here 

 identified, forms rather broad, bifoliate 

 branches 5 mm. or more in diameter, 

 frequently and irregularly dividing. 

 The surface is smooth but, unfike the 

 other branching Baltic species of the genus, distinct maculae are oc- 

 casionally developed. The zooecia are large, oval, thick walled, and 

 have a conspicuous peristome; three zooecia in 2 mm., measuring lon- 

 gitudinally, five rows of apertures in the same distance. The aper- 

 tures are arranged in rather regular longitudinal series which are most 

 interrupted when a macula is inserted. 



Fig. 65.— Pachydictya cyclostomoides. 

 Eichwald's vie'W of Micropoea cy- 

 clostomoides. a AND 6, feagment. 

 natural size, and a portion enlarged, 

 "Calcaire 1 Orthoceratites" Wesen- 

 berg, ESTHONIA. 



mi 

 0Hu4f 



YiG. 66.— Pachydictya cyclostomoides. o, tangential section, X20, showing the large oval 

 zocecia; 6, vertical section, X20. Je"we limestone (D1), St. Mathias, Esthonia. 



The internal structure is that of a typical PacJiydictya. In tangen- 

 tial sections the large size of the zooecia and the wide end spaces 

 separating them are the important features aside from the ring-Hke 

 walls. Vertical sections show a few diaphragms in the zooecial tubes 

 and a profuse development of vesicles and laminated tissue in the 

 interzooecial spaces. 



