MONOGRAPH OP THE EXISTING CR1NOIDS. 677 



found associated with the crinoids. The most complete account of these organisms 

 is that published by Cuenot in 1891. 



The unicellular organisms associated with the echinoderms are the following: 



DINOFLAGELLATA. 



Suborder ADINIDA. 

 Family PROROCENTRIDJE. 



PROROCENTRrM MICANS (EHRBNBERG). 



Perrier was the first to find a species of the genus Prorocentrum in the intes- 

 tinal tract of Antedon bifida, the announcement of his discovery having been 

 made in 1889. 



Cuenot states that when an Antedon is cut into serial sections there are found 

 in some special diverticula of the intestine which never contan food particles a 

 great quantity of these organisms heaped together and almost completely filling 

 the cavities of the diverticula. They are truly parasitic, and are always found in 

 these intestinal diverticula in all specimens examined. They attain a rather con- 

 siderable size, being up to 80 p. in length, and a large number are always found 

 in process of division. But their parasitism is only temporary, and little by little 

 thej^ escape from the body of the host. Some are always to be seen in the intestine 

 itself among the food particles which have not undergone any alteration. 



This species has long been known as a free-living organism. 



It is recorded as a parasite from Antedon bifida taken off the Isle of Man, and 

 at Roscoff, Concarneau, and other places on the French Atlantic coast. 



It is not known to occur in the Mediterranean species of Antedon, though 

 Cuenot looked for it in A . mediterranea. 



PROROCENTRUM DENTATUM STEIN. 

 PROROCENTRUM ROSTRATUM STEIN. 



These species were found by Stein in the intestines of salps, ascidians, and 

 comatulids. 



Prorocentrwn, sp. Cuenot. Found in the ambulacral grooves of Echinaster 

 sepositus (Lamarck) from Roscoff and Banyuls. 



CILIATA. 



Order TRICHOSTOMATA. 



Suborder ASPIROTRICHA. 



Family URONEMID^E. 



Uronema echini (Maupas). Found in the intestine of Paracentrotus lividus 

 (Brandt) in the Mediterranean. 



Uronema digitiformis (Fabre-Domergue). Found in the mucous on the skin 

 of M ' arthasterias glacialis (O. F. M tiller). 



