424 ZOOLOGY. 
telephone. Slight excitations provoked a short croaking 
. sound. ach of the small discharges was composed of a 
dozen fluxes and pulsations, lasting about one fifteenth of a 
second. The sound got from a prolonged discharge, how- 
ever, continued three to four seconds, and consisted of a sort 
of groan, with tonality of about mi (165 vibrations), agree- 
ing pretty closely with the result of graphic experiments. 
Marey has also studied the resemblance of the electrical 
apparatus of the electrical ray or torpedo and a muscle. 
Both are subject to will, provided with nerves of centrifugal 
action, have a very similar chemical composition, and re- 
semble each other in some points of structure. A muscle in 
contraction and in tetanus executes a number of successive 
small movements or shocks, and a like complexity has been 
proved by M. Marey in the discharge of the torpedo. 
The sting-rays (7rygon) have no caudal fin, but the spinal 
column is greatly elongated, very slender, and armed with a 
long, erect spine or “sting.” Some live in fresh water ; 
several species of sting-rays (Potamotrygon) inhabit the large 
rivers of Brazil and Surinam, as the Amazon, Tapajos, Ma- 
deira, and Araguay, digging holes in the sand, in which they 
lie flat and await their prey. In this connection it. may be 
said that Raja fluviatilis of India has been taken near Ram- 
pur, nearly 1000 miles above tide-reach. 
Mytobatis has the teeth forming a solid plate or pavement. 
The devil-fish (Cephalopterus diabolus Mitchell) of the coast 
of South Carolina and Florida is the largest of our rays, be- 
ing eighteen feet across from tip to tip of its pectoral fins, 
and ten feet in length, weighing several tons. It sometimes 
seizes the anchors of small vessels by means of the curved 
processes of its head and swims rapidly out to sea, carrying 
the craft along with it. 
Order 2. Holocephali.—This small but interesting group 
is represented by Chimera of the north Atlantic, and Cal- 
lorhynchus of the antarctic seas. In these fishes the four 
gill-openings are covered by an opercular membrane ; thus 
approaching the true bony fishes, and there are but four teeth 
in the upper and two in the lower jaw. The brain of Chi- 
mara is said by Wilder to combine characters of those of 
