56 FOSSIL MEDUS#. 
MEDUSINA RADIATA Linnarsson (sp.). 
>], XXVIII, fig. 2. 
Astylospongia radiata Linnarsson, 1871. Kongl. svensk. Vet.-Akad. Handl., vol. 9, 
No. 7, p. 13, Pl. II, figs. 15, 16. 
Medusites radiatus Nathorst, 1881. Kongl. svensk. Vet.-Akad. Handl., vol. 19, No. 1, 
p. 25, Pl. VI, figs. 1, 2. 
Medusites radiatus Matthew, 1890. Trans. Royal Soc. Canada, Vol. VIII, See. IV, p. 
141. 
Medusites radiatus Walcott, 1891. Tenth Ann. Rept. U.S. Geol. Survey, Part I, PI. 
LVI, figs. 2, 2a. 
Medusites cf. radiatus Pompeckj, 1896. Die fauna des Cambrium yon Tejrovie und 
Skrej in B6bhmen. Jahrbuch K.-k. geol. Reichsanstalt, vol. 45, parts 2 and 3, 
p. 501, pl. 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 40™" and 50™", but sometimes both 
larger and smaller specimens are found. Fig. 15' represents one of the largest, with a 
diameter of 60™™, fig. 161, one of thesmallest. 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 filled 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 lamelle 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. 
' Figs. 3 and 2 of Pl. XXVIII of this monograph. 
