J 66 NEW YORK STATE MUSEUM 



tegmen, or a specimen of Onychaster between the arms and coiled 

 around the anal tube. This, so far as we know, is the first instance 

 in which a Platyceras has been found in contact with a Crinoid 

 with a long anal tube; in all cases heretofore noticed the Crinoid 

 had an anal opening directly through the tegmen, and the Gas- 

 tropod was fastened invariably with the anterior portion of the 

 shell over the opening. This led to the supposition, for which 

 there seemed to be good reasons, that the ^[ollusk obtained its 

 nourishment, in part at least, from the excrements of the Crinoid. 

 This, however, was impossible in the case before us, where the 

 anal tube, with the anus at the distal end, extends out far beyond 

 the tips of the arms, and, so far as observed, bends abruptly to 

 one side, so that neither the opening nor the refuse matter could 

 have been in contact with the Mollusk. 



In more frequent association with this Actinocrinus is the 

 Onychaster, and it is worthy of note that this species of ophiuran 

 is rarely found by itself. Nor has it been observed at Indian 

 Creek on any of the other Crinoids, while at Canton it appears also 

 on most of the specimens of Scytalocrinus robustus (Hall), 

 a species with a large ventral tube, and the anus located far down 

 at the anterior side; but with this exception we have not seen it 

 on any other species. The fact that this Ophiurid is only found 

 associated with certain species, and there always under similar 

 conditions, and the frequency of this occurrence, would seem to 

 indicate that the position between the arms of these crinoids was 

 its favorite resting place, in which it either found protection, or 

 some special facility for obtaining nourishment. 



These specimens are from the Crawfordsville limeshale of the 

 Lower Carbonic (Mississippian). 



Crinoids and Myzostomum 

 All the known living species of the minute wormlike creature 

 Myzostomum (60 to 70 in number) are parasitic on the crinoids 

 whereon they form galls or swellings by the overgrowth of the 

 test. Similar galls have been noted on both Mesozoic and Paleo- 

 zoic species of crinoids by Bather, Shipley, Fraas and other 

 writers, and they are generally ascribed to the Myzostoma. 



Coral on a Coral 



The case of Caunopora. It is now quite generally conceded that 

 Caunopora which has commonly been regarded as a hydroid coral 

 like Strom.atopora,but with sharply defined, definitely walled tubes, 

 is actually a laminate hydroid overgrowing a series of erect tubes 

 like those of Syringopora or Aulopora, carrying oblique dis- 

 sepiments within. Caunopora placenta Phillips is a 

 Devonic species. 



