148 Review of Recent Geological Literature. 
vol. vii., noticed above. It contains descriptions and illustrations of Ptero- 
poda, Cephalopoda and Annellida. The Annellida were not embraced in 
the original plan of volume v. They are here introduced for the sake of 
comparing typical forms of Tentaculites with certain species, chiefly from 
the Hudson River group, that have from time to time been referred to the 
genus Te7itaculites and with other more or less closely related forms. The 
large amount of material in the hands of the author afforded unusual facil- 
ities for making such comparisons. 
The result of the comparison has been to lead Professor Hall to the con- 
clusion that the Lower Silurian Tentaculites are not Tentaculites at all. 
Moreover, many of the genera and species that palaeontologists have been 
laboring industriously to establish, emerge from the investigation with 
scant claim for further recognition. For example, the author claims that 
the material in his possession demonstrates that the following forms are 
simply difEerent stages of development of what appears to be a single 
species of the genus Cou-sviATEsl Spirorhis cincimiatiensis, Ortonia minor, 
0. cornea, Concliicolites corrugatus, Tentacidites sterling ens is, T. richmonden- 
sis,Coi'nulitesflexuosus,C.immaturus,C'.incurvus, C. distans, C. clintoni, 
C. arcuatus, O.proprius, C. hellistriatus, C. crysalis, C. cingulatus and C. 
tribulus. 
The larger part of the supplement is devoted to Cephalopoda. Twenty 
species, not illustrated in vol. v., part ii., are here described, together with 
a number previously described, but here described and figured from new 
material illustrating features additional to those before illustrated. 
On the attachment of Platyceras to Pakmcrinoids, and its Effects in Modi- 
fying the Form of the Shell. By Charles R. Keyes. This paper, embrac- 
ing fifteen pages of descriptive matter, illustrated by one plate, was read 
before the American Phosophical Society October 19, 1888. The fact that 
Platycerata occur attached to the bodies of crinoids has long been known. 
The fact that they always occur in a particular way, with the anterior part 
of the aperture covering the ventral opening of the crinoid, is one of com- 
paratively recent recognition. The situation of the anal opening in cri- 
noids is such that the attached shell is often embraced by the arms, and 
this led the earlier observers to conclude that the crinoids fed on the gas- 
teropods, and that death sometimes overtook the predaceous echinoderms 
while they were in the very act of devouring their victims. Moreover, the 
earlier palaeontologists regarded the ventral opening as the mouth of the 
crinoid, and so far as the position of Platyceras with reference to this 
opening was noted at all, it only tended to confirm the belief in the car- 
nivorous habits of crinoids. A history of recorded observations on the re- 
lations of Platycerata to crinoids is given, and this is followed by an ac- 
count of the author's observations, made on an extensive series of illustra- 
tive examples in the magnificent crinoid collection of Wachsmuth and 
Springer. 
The observations of Keyes support the views entertained by a number 
of modern palaeontologists, to the effect: 1. That Platyceras, like Capu 
lus, was sedentary, attaching itself to foreign bodies and remaining fixed 
during life, 2. That the association of Platyceras to the crinoid to which 
