be THE DEPTHS OF THE SEA. [cHAP. 11. 
tubercle; and the two posterior ambulacra, with 
their ocular plates, meeting at another point and 
forming a kind of secondary apex. ‘The fifth genital 
plate is obsolete. The specially interesting point is 
that, while we had so far as we were aware no living 
representative of this peculiar arrangement of what 
is called ‘disjunct’ ambulacra, we have long been 
well acquainted with a fossil family, the Dysasteride, 
possessing this character. Many species of the 
genera Dysaster, AGASSIZ, Collyriies, DESMOULINS, 
Metaporhinus, MicuEuix, and Grasia, MIcHELIn, 
are found from the lower oolite to the white chalk, 
but there the family had previously been supposed to 
have become extinct. 
The next attempt was one of our very few entirely 
unsuccessful hauls, the dredge coming up empty. 
This we attributed to an increase of wind and swell, 
and consequent drift on the vessel, which seemed to 
have prevented the dredge from reaching the ground. 
We devoted the morning to a series of temperature 
soundings at intervals of 50 fathoms from the surface 
to the bottom, and this we accomplished in a very 
satisfactory manner, with results which will be fully 
discussed hereafter. After a rapid descent for the 
first 50 fathoms the next 150 fathoms maintained 
a high and a tolerably equable temperature, and 
there was then a rapid fall between 200 and 300 
fathoms, the thermometer at the greater depth indi- 
eating 0° C. From 300 fathoms to the bottom the 
temperature fell little more than a degree. ‘Thus 
the entire mass of water in this channel is nearly 
equally divided into an upper and lower stratum, the 
lower being an Arctic stream of nearly 2,000 feet 
