BIONOMIC CHARACTERS OF VERMES 1023 



be regarded as strangers which have drifted to their present posi- 

 tion ; in fact, it is often easy to see that such has not been the case 

 in any particular locaKty, from an examination of the shells them- 

 selves, as well as from the extraneous evidence. Thus, according 

 to Clarke (S'^33, ^t seq.), the ammonoids of the Naples beds of 

 western New York "... bear sufficient demonstration in 

 themselves that they have lived and died in these sediments." 

 Many of the most delicate shells retain their apertures unbroken, 

 and their suface ornamentation uninjured, a fact which is not con- 

 sistent with transportation by waves and currents. The presence 

 of the young in all stages of development further argues for an 

 indigenous occurrence. "On the other hand," says Clarke, "there 

 are excellent reasons for regarding the prenuncial Intumescens 

 fauna, that of the Styliola [Styliolina] limestone, as due to trans- 

 portation from some adjoining province not yet known to us." 

 The Goniatites of this fauna are associated with the millions of 

 holo-planktonic Styliolina, with floated logs, and probably other 

 pelagic organisms, and the sediment in which they were embedded 

 was such as probably was not conducive to the well-being of such 

 animals, so that their occurrence is best explained by the hypothesis 

 of flotation. 



Of the embryology of Nautilus, and hence of the whole group of 

 Tetrabranchiata, nothing is known. The Dibranchiata develop di- 

 rectly within the egg capsule, no veliger stage occurring. 



VI. Platylelmintha. VII. Vermes. 



These worms are marine, fresh-water, or terrestrial animals. 

 They belong chiefly to the benthos, though some marine forms lead a 

 partially nektonic existence, while others are typically planktonic. 

 Several oligochsetous annelids have become adapted to a marine 

 life, though the group is normally fresh-water or terrestrial. Among 

 the benthonic species all grades of a sedentary life are observable, 

 from the tube-building orders, which live permanently in attached 

 tubes, to those which only temporarily occupy a given area. Tubi- 

 colous worms, which, like Spirorbis, attach their tubes chiefly to 

 algae, may often lead an epi-planktonic existence when the algas are 

 torn from their anchorage and washed away by currents. 



A muddy bottom seems to be the favorite haunt of the littoral 

 species, except such forms as build attached tubes (e. g., SerpuHd?e, 

 etc.), which occupy stony and shelly bottoms. These latter often 

 build extensive reefs of interwoven calcareous tubes. 



