434 ZOOLOGY. 



telephone. Slight excitations provoked a short croaking 

 sound. Each 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 

 apjDaratus 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 {Trygon) 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 Raia fluviattlis of India has been taken near Ram- 

 pur, nearly 1000 miles above tide-reach. 



Myliohatis has the teeth forming a solid jilate or pavement. 

 The devil-fish {Cephahpterus diaholus 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. HolocephalL — This small but interesting group ' 

 is represented by Ohinicsra 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 Ohi- 

 msera is said by Wilder to combine characters of those of 



