MONOGRAPH OF THE EXISTING CRINOIDS. 645 



could not refer it to any species of that genus, or to any other of the ophiurans 

 ■which were obtained by the Challenger. It had a relatively large dorsocentral, 

 five small basals. and five large radials, the outer ends of which were tubercular 

 and fitted in between the two large radial shields, which were also more or less 

 tubercular on their line of junction. The arms extended outward between the 

 cirri of the comatulid and coincided in direction with its rays, while their ends 

 were more or less twisted around the bases of the cirri. The symmetrical arrange- 

 ment of the large primary plates on the ophiuran disk, together with the position 

 of the arms, gave a very singular appearance to the centrodorsal of the comatulid. 



OPHIORAN. 



H. C. Chadwick records that from a specimen of Heterometra savignii taken 

 at Ul Shubuk, Sudanese Red Sea, in nine fathoms which was whitish with a violet 

 tinge, with patches of darker color and of j'ellow, he took 15 ophiurans which 

 lived with their arms twisted around those of the comatulid, and that the color of 

 these on the whole resembled that of their host. 



OPHICIUN PI.UTEUS. 



Dr. P. H. Carpenter mentions finding an ophiuran larva attached by its long 

 pluteus arms to the column fragment of Metacrinus tuberosus which was dredged 

 by the Challenger off the Kei Islands, in 140 fathoms. He considers this associa- 

 tion as probably merely accidental. 



MOLLUSCA, 



GASTEROPODA. 



Professors Rene Koehler and Clement Vaney, of the University of Lyons, have 

 recently published a most excellent memoir upon the ectoparasitic gasteropods, 

 nearly all of which occur upon echinoderms. 



These parasites fall into four classes. The first comprises species belonging 

 to the family Capulidae. all included in the genus Thyca; the second is composed 

 of species belonging to the family Melanellidae, which are distributed in the genera 

 Melanella, Sahinella, Pelseneeria, Mucronalia, Stylina, Stilifer, Megadenus, and 

 Gasterosiphon ; the third is represented by the curious Ctenosculum described by 

 Heath ; and the fourth by two pyramidellids described by Pelseneer which are para- 

 sitic upon the lamellibranchs. 



None of the wormlike endoparasitic gasterpods, such as EntoconcJia, Enter- 

 oxenos, and Entocolax, are known to occur in the crinoids. 



Of the echinoderms the starfishes most frequently support ectoparasitic gaster- 

 pods, and upon them occur species of the genera Thyca, MelaneUa, Mucronalia, 

 Stilifer, and CtenoRculum, nearly all of the records being from the East Indian 

 region. 



Next to the starfishes the crinoids appear to be the most subject to this form 

 of parasitism, and upon them occur species of the genera Stilifer, StyUna, SabineUa, 



