SABELLIDES AND SERPULIDES 259 



they are retained only as sectional ones in the following table (p. 261) , 

 especially as setae of similar forms are found in genera which differ 

 from Spirorbis in the number of thoracic segments, in the form and 

 substance of the plate in the operculum, and in some instances in 

 lacking an operculum. 



As a large number of species are known only by their tubes, the 

 animals of comparatively few having been studied with reference to 

 the form of their collar setse, two simple methods have been adopted 

 in grouping them, as a possible aid to their correct identification : One 

 based on a knowledge of the tube (see p. 260), and the other on the 

 form of the superior collar setae (see p. 261). 



Levinsen (1883) used the terms 4 sinistral ' and * dextral' in group- 

 ing the northern species, but also retained (after Morch) the sub- 

 stance 1 of the tube as an equally important character. As this, how- 

 ever, is found to change sometimes with growth, and also to be more or 

 less affected in preservation, it cannot always be defined with accuracy, 

 and might prove misleading. Therefore the direction of the coil and 

 the character of the surface of the tube are the only points considered 

 in the first table. 



To avoid repetition and confusion of names, a list of all the recog- 

 nized species, as far as known, is given after the two tables. They 

 are arranged chronologically, and with each is given its principal 

 synonyms and reference to figures, also the principal localities at which 

 it has been found. As the numerals used by Caullery and Mesnil in 

 their recent and very important work (1897) show the arrangement of 

 species in their subgeneric relation as well as to one another, this num- 

 ber is given after the names of these authors. Names with an asterisk 

 show that the species has been studied and is in the Yale University 

 Museum. 



Of the 73 species cited, only 59 could be placed in the first table, 

 although the position of some of these may be questioned, and but 41 

 in the second table. The necessary further study of the others may 

 prove some of them to be but synonyms there being 14 species having 

 the tube inadequately described and 32 about which nothing is appar- 

 ently known of the animal. 



'Crystalline, vitreous, cretaceous, porccllanous, etc., have been used. 



