[MATTHEW] ACROTHYRA AND HYOLITHES 101 
features from the Brachiopoda. It would seem that the Tube Worms 
afford the nearest living analogues to this group of forms, which 
reached back .to the earliest Paleozoic time. 
For those who wish to look into this matter more fully the follow- 
ing notes from authorities, and descriptions of species are given. 
To the industry and zeal of Joachim Barrande, naturalists owe 
much of our present knowledge of the Hyolithidæ ; and to him also 
that these fossils have for so many years been referred to the Pteropoda. 
That this reference needs revision some leading writers are now agreed, 
but none seem to suggest a suitable relation. That they are not Brachio- 
pods seems indicated by this investigation, though it may be remarked 
that the late Sir William Dawson called attention to the similarity 
between the two groups in the structure of their shells. If they are not 
Annelida as the writer has suggested, since they differ considerably 
from the modern Tube worms, there remains the alternative that they 
are a branch from the worms related to, but independent , of the Brachio- 
poda. 
BARRANDE. 
In his System Silur. de la Boheme, vol. IIT., Pteropoda, this author 
figures the following :— 
PLATE 10, Figs. 27 to 29. Shows several views of the opercule of 
Hyolithes maximus of the Paradoxides beds. This is a characteristic 
example of an opercule showing the broad “chevron” or rafter, behind 
the cone, and the broad horizontal limb: there are two muscle-pits behind 
the apex. The radiating (vascular?) lines on the horizontal limb are 
about thirteen on each side—a large number. 
HOLM. 
Dr. Gerhard Holm’s memoir shows two of the three types of oper- 
cula found at St. John in the Paradoxides beds. The best examples of 
opercula from Sweden were found in the Par. Tessini zone (=P. Abena- 
eus at St. John). Some of those from P. Œlandicus and P. Forch- 
hammeri zones show forms resembling those from St. John. 
The large opercula from that country are represented on Tafl. 1, 
Fig. 88, and Tafl. 5, Fig. 47. The medium sized opercules with high 


1 Introduction to the Study of the Brachiopods. Hall & Clarke, pl. 5, 
figs. 12 and 15. 
