56 FOSSIL MEDUSA. 



Medusina radiata Liiinarsson (sp.). 

 "1. XXVIII, fig. 2. 



Astylosppngia radiata Linuarsson, 1871. Kongl. sveusk. Vet.-Akad. Handl., vol. 9, 



No. 7, p. 13, PI. II, figs. 15, 10. 

 Medusites radiatus Nathorst, 1881. Kongl. sveusk. Vet.-Akad. Handl.. vol. 19, No. 1, 



p. 25, PI. VI, figs. 1, 2. 

 Medusites radial us Matthew, 1890. Trans. Royal Soc. Canada, Vol. VIII, Sec. IV, p. 



141. 

 Medusites radiatus Walcott, 1891. Tenth Ann. Kept. I ". S. Geol. Survey, Part I, PI. 



LVI, figs. 2, 2a. 

 Medusites ef. radiatus Pompeckj, 1890. Die fauna des Canibriuni von Tejrovic und 



Slrrej in Boh men. Jahrbuch K.-k. geol. Reichsnnstalt, vol. 15, parts 2 and 3, 



p. 501, pi. 14, fig. 3. 



The original description is printed in Swedish and the volume contain- 

 ing it is accessible to but few students; therefore a translation is given: 



A disk shaped sponge, varying to hemispherical, with nearly regular circular 

 periphery. The diameter is generally between 10""" and 50 ram , but sometimes both 

 larger and smaller specimens are found. Fig. 15 ' represents oue of the largest, with a 

 diameter of 00""", fig. 10 ', one of the smallest. The lower side is generally almost hemi- 

 spherical, and this seems to be its natural form, but sometimes it is found nearly flat, 

 probably owing to pressure. It always appears smooth, without any trace of structure. 

 No attachment surface is ever visible, and hence, supposing that this is really the 

 lower side, the sponge must have been free. The upper side, near the periphery, is 

 generally almost level. At times it is so all over, but ordinarily it rises gradually 

 inward until it is interrupted by a circular opening the diameter of which is about 

 equal to half the diameter of the whole sponge. This opening probably led down to 

 a funnel- or cup-shaped depression, which, however, is at present always tilled with 

 rock mass, so that its structure can not be observed. Between the opening and the 

 periphery of the sponge, there run numerous narrow, radiating ridges. When the 

 upper surface is level, they are nearly straight, simple, or in the form of strings of 

 pearls. When the upper surface is raised, they appear more irregular, curling and 

 anastomosing, while the string-of pearls appearance becomes more and more smoothed 

 out, a difference which, however, should not induce the establishment of several spe- 

 cies, since transition forms are not wanting. Perhaps the upper side of the sponge 

 was covered with a kind of epidermis. On some stone slabs there is seen the upper 

 surface of some specimens, in all of them level and ornamented with regular, radiat- 

 ing, string-of- pearl lines. Small lamella? of that surface occasionally come off, and 

 their lower side is found ornamented in the same way as the upper, leaving under 

 them an impression consisting of radiating depressed lines with dot like depressions. 



: Fins. 3 and 2 of PI. XXVIII of this monograph. 



