NO. 5 MIDDLE CAMBRIAN ANNELIDS 121 



tube is usually so completely flattened that the fine concentric lines 

 and fine ridges that give an annulated appearance to it have dis- 

 appeared ; often the tubes appear to be longitudinally striated as the 

 result of lateral compression. Some tubes appear to be slightly con- 

 stricted near the aperture and also a little thickened. The tubes 

 were thin and easily compressed and flattened. They may have 

 been calcareous, but from their bright, almost shiny, luster they were 

 more probably chitinous or parchment-like. 



Dimensions. — The largest flattened tube has a length of 68 mm., 

 with a width of 12 mm. at the larger end, and of 8 mm. at the 

 smaller. A more slender tube 64 mm. long is 9 mm. wide at the large 

 end and 2 mm. at the smaller. The larger number of tubes have a 

 transverse diameter of from 5 to 7 mm. at the larger end. 



Animal. — Ten specimens show more or less of the animal pro- 

 jecting from the tube. It fills the end of the tube and is divided 

 into sections a little longer than wide that are faintly indicated by 

 slight sviccessive contractions, and the presence of somewhat more 

 prominent spines or hooks. The spines appear to have been ar- 

 ranged in concentric rows over all parts of the surface of the body 

 except the terminal section. A specimen that is not illustrated shows 

 a conical terminal section with several small-jointed appendages 

 about its posterior end. My present impression is that the terminal 

 section represents the head and the appendages a circle of gills. 

 From the fact that the animal projects so much more from some 

 tubes than it does from others, it seems that it was retractile and 

 could withdraw into its tube. No traces of an operculum have been 

 seen. With the' somewhat formidable series of spines to protect it 

 an operculum would scarcely have been necessary. 



Obscrrations. — On pi. 19, fig. 7. there is inserted for comparison 

 with Selkirkia major a photograph of a specimen of Hyolithes cari- 

 natus Matthew showing the triangular tube, operculum, and, for 

 the first time among the Hyolithidfe, the curved supports of the 

 fins of apteropod. 



The discovery of the animal that lived in one of the tubes that has 

 been classed with the pteropods removes one more doubtful form 

 from the latter to the annelids, and with it will probably go Hyo- 

 litJiellus and other tube-like shells that have none of the distinctive 

 external characters of Hyolithes and its allies. 



In these preliminary notes I do not care to mention further the 

 relations of the various Paleozoic tube-like fossils that have been 

 referred to the Pteropoda and Annelida, except to call attention to a 



