924 General Notes. 
theses. Through these heavier materials conduction is rapid, and 
the maximum is easily maintained. Mark! I saya portion of the 
centre, for the centre is unquestionably solid, as a resultant of 
pressure, the temperature being the maximum attained at the point 
of liquefaction. As the inner portion consists of the heavier 
materials, which are also far better conductors of heat, and ren- 
dered still better conductors under the immense pressure of the 
superincumbent materials, this solid nucleus will maintain, by con- 
duction, this maximum temperature throughout. Finally, it may 
not be void of all interest to take a very brief view of earth’s 
outer envelop. 
The entire outer shell, as all know, consists mainly of two 
persistent gases—oxygen and nitrogen ; oxygen, a constantly active, 
ever varying, yet constantly nearly the same in proportion; and 
nitrogen, a neutral dilutent for the active oxygen. With these 
two are mingled a few other substances, most conspicuous of which 
is watery vapor. 
Next is a shell—a little broken—of water. This is followed, 
in the descending order, by a shell of mingled substances, the 
common rock materials. These are very poor conductors of heat. 
The lighter of these materials do not form a very thick mass. 
As the entire mass of earth, including all these, has a much higher 
specific gravity than any of these, it follows that heavier materials 
soon begin to take the place of these; nevertheless, this outer 
envelop must be sufficient to protect the heated nucleus, and volcanic 
emissions show that their seat is not below this outer shell, but in it. 
—Ira Sayles, Ithaca, N. Y., March 12, 1888. 
(To be continued.) 
THE ATTACHMENT OF PLATYCERATA TO Foss, CRINOIDS has 
been long known, but the hitherto extreme rarity of illustrative 
specimens has necessarily occasioned only brief explanatory remarks. 
nasmuch as the gasteropod shell was invariably situated on the 
crinoidal vault, and covering the ventral opening, which was erro- 
neously regarded as the mouth of the crinoid, conclusive evidence 
of the carnivorous habits of the crinoideans was thought to be 
established. Other explanations were from time to time offered, 
but for the most part they were also fallacious, and originated in 
wrong conceptions relative to the true functions of certain structures 
l the group of echinoderms. Opportunity has recently 
offered for the examination of an extensive series of palæocrn- 
oids with attached Platycerata, embracing numerous specimens of the 
following species: Ollacrinus tuberosus Lyon and C., O. typus Hall, 
Physetocrinus ventricosus Hall, Strotocrinus regalis Hall, Doryormus 
immaturus Wachsmuth and Springer, Marsupiocrinus cælatus £ hit- 
