8 FOSSIL MEDUSZ. 
RELATION TO OTHER FOSSIL MEDUS#. 
Since the publication of the notes on the Lower Cambrian medusz, in 
1891, much more has been learned respecting the Middle Cambrian forms; 
and it now appears to be possible to establish a family relation between the 
Lower Cambrian Dactyloidites asteroides and the Middle Cambrian genera, 
Brooksella and Laotira. The specimens of Dactyloidites are usually pressed 
out flat in the lamine of the slates, only a thin film remaining as a dark 
stain on the slate. (See Pl. XXVI.) In one instance some fine sand was 
mixed with the argillaceous mud, and on a single large slab a few specimens 
are a little convex. One of the best of these is shown by fig. 2 of Pl. XXIV. 
It is a beautiful specimen, in which the interior radial canals are indicated 
within an inner portion of the lobes, which is separated from the dark sur- 
rounding slate by a semitranslucent outer part of the lobes that strongly 
resembles the sarcode of a recent medusa. Fig. 1 of Pl. XXV is another 
somewhat convex specimen, but it does not show any traces of the interior 
structure. With the exception of fig. 2 of Pl. XXIV, all the specimens of 
Dactyloidites are very much compressed and distorted. For comparison 
with Laotira cambria, compare fig. e of Pl. XXVI with fig. 5 of Pl. XXII; 
fig. d of Pl. XXVI with fig. 6 of Pl. VI; fig. 1 of Pl. XXV with fig. 10 of 
Pl. V; and fig. 2 of Pl. XXIV with fig. 2 of Pl. XXI. 
The foregoing comparisons, and many others that can be made with 
the abundant material in the collections, establish the relation between the 
Middle Cambrian genera and Dactyloidites. Of the two genera, Brooksella 
appears to be nearer the latter than does Laotira. 
To the Lower Cambrian species of Sweden there is little apparent 
similarity outside of their ordinal or subordinal relationship in belonging 
to the Discomedusze. This applies to Medusina costata and M. princeps. 
The position of M. radiata is mach more doubtful. 
The well-identified Jurassic species are referred by Dr. Ammon to the 
Discomedusze and the suborders Semostome and Rhizostome. Except that 
the Middle Cambrian species may possibly belong to the Rhizostomze, and 
that three of the Jurassic are referred to the same, there appears to be no 
opportunity for further detailed comparison. The transverse vertical section 
1Fauna of the Lower Cambrian or Olenellus zone: Tenth Ann. Rept. U.S. Geol. Survey, pp. 587, 605, 606. 
