298 Mr W. Bateson, Suggestion that Bilobites, dc. [Nov. 12, 
(6) On a machine for describing an Equiangular Spiral. By 
Horace Darwin, M.A., Trinity College. 
The curve is traced by an inked wheel, which is set obliquely 
on the bar which forms the radius vector, and rolls on the paper. 
November 12, 1888. 
Mr J. W. CLARK, PRESIDENT, IN THE CHAIR. 
C. W. C. Bartow, B.A., Peterhouse, was elected a Fellow. 
The following communications were made to the Society : 
(1) Kzhibition ef photographs of the image formed on the 
retina by an electric lamp. By Mr FRIESE-GREEN (communicated 
by Mr R. T. Glazebrook). 
(2) Suggestion that certain fossils known as Bilobites may 
be regarded as casts of Balanoglossus. By W. Bateson, M.A., 
St John’s College. 
The author stated that he had by chance seen specimens of 
these fossils, which occur in the Carboniferous series, in the 
Woodwardian Museum, and had been struck by the resemblance 
which they bore to Hnteropneusta. He had subsequently, by 
the kindness of Professor Hughes, been permitted to examine 
his large collection of these forms, and had also brought together 
additional specimens from the place in Westmoreland where 
Professor Hughes had discovered them. 
The likeness which these fossils bear to Balanoglossus, in size 
and surface-markings, is very close, and they are practically a 
representation in stone of the generative region of that animal. 
The author suggested therefore that they had been formed 
as casts of the closely fitting tube of mucus and sand which 
envelopes parts of the larger species of Balanoglossus. He par- 
ticularly called attention to a specimen which was apparently 
a cast of the body at the junction of the generative and intestinal 
regions. The fossils are of considerable length, varying up to 
about two feet. Balanoglossus is the only animal having a 
comparable structure which reaches such a length. Two species 
were exhibited of the fossil form which differed from each other 
very much as B. salmoneus (Giard) differs from B. Robiniw (Giard). 
The texture of the sandstone was exactly that of the sand at 
the Glenans Islands where these two forms now occur. In some 
specimens, as pointed out by Professor Hughes, there were in- 
dications that the animals had lived immediately under the 
surface of the sand, which is not the case with existing forms. 
The author wished to express his thanks to Professor Hughes 
for his assistance in this investigation. 
