646 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



and Melanella; Stylina is known only from the Mediterranean, and Sabinella, as a 

 parasite on crinoids, from Ceylon, Singapore, and the Queen Charlotte Islands; 

 Stilifer and Melanella occur both in the Atlantic and in the Indo-Pacific. 



G aster osiphon, internal and without a shell, though fundamentally an external 

 parasite, is found in a deep-sea holothurian. Megadenus, truly parasitic, and 

 exhibiting a very marked sexual dimorphism, lives upon the arborescent tentacles 

 of a species of the genus Holothuria in the West Indian region. In another species 

 of the same genus in the East Indian region Melanella has been found attached to 

 the external surface and in the buccal cavity ; while in a third species on the coast of 

 Norway a species of Melanella is found in the digestive tube, where, however, it is 

 scarcely more than a commensal. 



Several species of Stilifer, and especially of Pelseneeria, have been found 

 upon echinoids, mostly from deep water, both in the Atlantic and in the Pacific, 

 and the genus Mucronalia has been reported from two ophiurans, Ophiothrix 

 crassispina Krchler from the Dutch East Indies in 274 meters, and 0. deposita 

 from the same region in 310 meters. 



We know nothing whatever of the habits of the gasterpods occurring on the 

 crinoids: as found they are always very firmly attached to the hosts, but, on the 

 other hand, the frequent presence of perforations in the calyx in addition to those 

 covered by the shells appear to indicate that they are not permanently fixed in one 

 position, but possess the power of changing their location. 



In 18b8 Count Pourtales wrote that among the small stalked crinoids dredged 

 in 237-306 fathoms off the Samboes and off Sand Key, Florida, an)d referred 

 by him to B ' ourgueticrinus hotessieri (a species of Bythocrinus), he found one 

 which had three small examples of a species of Stilifer adhering to the outside of 

 the calyx, and that small round holes, bored probably by these parasitic molluscs, 

 could be seen also in the calices of some of the others. 



In 1875 Prof. Ludwig von Graff, who at that time was engaged in his studies 

 upon the Myzostoma, found upon Antedon mediterranea a small gasteropod, which, 

 truly parasitic, is attached to the anal tube or pinnules into which it bores a hole. 

 He called it Stylina comatulicola. 



In 1877 Sir Wyville Thomson mentioned two specimens of "Rhizocrinus lofo- 

 tensis " dredged by the Challenger off Cape Agostinho, Brazil, each of which was 

 infested with several specimens of a species of Stilifer, and in 1884 Dr. P. H. Car- 

 penter, evidently having in mind the records of Pourtales and Thomson, wrote that 

 Rhizocrinus lofotensis is often infested with two or three small shells of Stilifer, 

 which bore comparatively large holes in its calyx. 



In 1895 Dr. Clemens Hartlaub figured a parasitic gasteropod attached to 

 an undetermined comatulid, apparently a species of Rathymetra, from the Gulf of 

 Panama. He states that it is related to Stilifer and according to Professor von 

 Martens is apparently a Mucronalia. 



On the specimens upon which I based the new species Ptilocrinus pinnatus I 

 found a number of parasitic gasteropods, which Dr. Paul Bartsch described in 

 1907 under the name of Eulima ptilocrinicola. 



