THE FOSSIL ANNELID GENUS HAMULUS MORTON, AN 

 OPERCULATE SERPULA. 



By Bruce Wade, 



Of the Tennessee State Geological Survey. 



INTRODUCTION. 



Among some of the recent discoveries in the large and well-pre- 

 served Ripley Fauna of the Upper Cretaceous at Coon Creek, McNairy 

 County, Tennessee, are a number of opercula from the Serpula Hamu- 

 lus Morton. Species of this genus are widely distributed in the Cre- 

 taceous, but if the opercula have ever been found previously they 

 are still unknown in the literature; so it is the purpose of this brief 

 paper to describe one new species and the calcareous opercula from 

 two species of this interesting group of fossil annelids. 



This paper is published by the permission of Wilbur A. Nelson, 

 State Geologist of Tennessee. 



GENERAL REMARKS. 



The Sea-worms or Polychaeta included in the suborder Tubicola 

 are distinguished by the fact that they inhabit variously formed 

 tubes, to which they are not organically connected, and in which they 

 can move freely by means of their setigerous foot tubercules. Owing 

 to their possession of an investing tube branchiae are only developed 

 in the anterior region of the body, this being the only part which 

 is ordinarily exposed to the action of sea water; hence the Tubicola 

 are sometimes called the " cephalo-branchiate " Annelids. 1 



The protecting tube of the Tubicolar Annelids may be composed of 

 calcium carbonate, of grains of sand, or other foreign matter, or of 

 chitinous material. When the tube is calcareous it presents certain 

 resemblances to the shells of some of the Mollusks, such as Vermetus, 

 Dentalium, or certain of the Rudistes. In the living state it is easy 

 to make a distinction between these, for the Tubicolar Annelids are 

 in no way organically attached to their tubes, whereas the Mollusks 

 are always attached to their shell by proper muscles. In the fossil 

 condition, however, it may be very difficult to refer a given calcareous 

 tube to its jjroper place. As a general rule, however, the calcareous 

 tubes of Annelids, such as Serpula, are less regular and symmetrical 



1 Nicholson and Lydekker, Manual of Palaeontology, ed. 3, vol. 1, Edinburgh and London, 1889. 



Proceedings U. S. National Museum. Vol. 59-No. 2359. 



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