Keyes. ] 234 [Oct. 19, 
Cromyocrinus simplex. He remarks that the gasteropod was attached to 
the anal plate crowded between the arms of the crinoid, and that very 
probably the Capulus was dependent for its food upon the crinoid, or per- 
haps fed upon the excrementitious matter. The closely allied Cromyo- 
crinus gemmatus had not been found with the Capulus affixed. 
1868. Meek and Worthen* in their notes on the Structure and Habits 
of the Paleozoic Crinoids refer to the attachment of Platycerata to two 
species of Crawfordsville, Ind., crinoids. Their remarks also appear in 
the American Journal of Science+ and in the report of the Illinois Geo- 
logical Survey.{ The somewhat prolix discussion there presented, how- 
ever, is directed more toward the real functions of the vault aperture in 
the crinoid than to the Platyceras itself. Special mention is made of 
Platycrinus hemisphericus Meek and Worthen and Ollacrinus tuberosus 
Lyon and Casseday from the Keokuk of Indiana. It was observed that 
Platyceras infundibulum M. & W. was usually attached to the former spe- 
cies, and that the anterior side of the mollusk was always directed upward, 
while in regard to, the latter species ‘‘it is worthy of note, that it is always 
another, subspiral, Patyceras (very similar to P. equilaterum) that we 
find attached to this crinoid, so that here, at least, it would seem that each 
of these two crinoids has its own particular species of Platyceras.”’ It is 
also here shown that the contact of the gasteropod and crinoid is more 
than transient, as the sinuosities of the margin of the shell is adapted ex- 
actly to the irregularities of the surface of the crinoid. 
1869. EE. Billings$ in answering some objections urged against his 
views on the structure of the crinoidea, etc., supposes that when the Platy- 
ceras covers the ventral opening, which he regards as the mouth, there 
must have been space left for a stream of water to pass under the edge of 
the shell into the mouth of the crinoid. He adds: “ The view I took of 
the subject in my paper was that the gasteropod ascended the stalk of the 
crinoid and thrust its proboscis into the mouth of the latter. The crinoid 
then slowly drew its arms together and held the shel] fast until both 
died.’’ ‘ 
1879. Wetherby,| describing some new species of crinoids from the 
Kaskaskia group of the Subcarboniferous, states that all of the specimens 
of Pierotocrinus acutus Weth. and P. bifurcatus Weth. have a gasteropod 
resting on the vault. 
1879. H. Trautschold{ figured and redesciibed Cromyocrinus simplex 
Trauts. with a Platyceras attached. “He suggests that the process on the 
anal side was built by the crinoid for protection against the parasitic mol- 
lusk, but adds that the gasteropod may have fed on the refuse matter of 
the crinoid. 
*Proc. Acad. Nat. Sci. Phila., 1868, p. 340, et seq. 
f 2d Series, July, 1869, p. 25, ef seq. 
ft Vol. v, 1873, p. 834. 
#Am. Jour. Sci. (2), Vol. xlix, p. 235. 
| Jour. Cincinnati Soc. Nat. His.. Oct., 1879, p 2. 
{ Die Kalkbriiche yon Mjatschkowa, p. 119, Moskau, 1879. 
