42 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



than those of Vermetus, while the latter are partitioned by shelly 

 septa, which do not exist in the former. Again, the tube of Dentalium 

 is open at both ends, whereas it is closed at one end of the Serpula. 

 In the Annelidous genus Ditrupa, however, the tube is open at both 

 ends, so that this distinction is one not universally applicable. 

 The tubes of the serpuloid genus Hamulus are quite regular and 

 symmetrical and its species have frequently been described as Dentalia. 

 Tubes of certain species of Hamulus together with their opercula have 

 a superficial resemblance to certain species of Rudistes such as Radio- 

 lites lombricalis d'Orbigny 2 and Hippurites variabilis Munier Chalmas 3 

 from the Upper Cretaceous of France. The apophyse of the oper- 

 culum of Hamulus resembles very much the apophyse of the upper 

 valve of certain of the Rudistes, but the operculum of Hamulus is 

 truly an operculum of a circular aperture, while the upper valve of 

 the Rudistes does not fit into a circular cavity of a lower valve. 

 Another difference is the absence of any evidence of muscular attach- 

 ments on the inner surface of the tubes of species of Hamulus. 



The operculate form Hamulus onyx Morton is probably related to 

 some such form as the existing species Serpula contortuplicata 4 (pi. 9, 

 fig. 4) . There are existing quite a group of Serpulas with calcareous 

 opercula; these are the Vermilias that are still abundant along the 

 sea coasts to-day. Existing species with chitinous opercula are quite 

 common and some of the forms that may be cited as analogous to 

 Hamulus onyx are Enponatus dipona Schmarda and Pomatoceros tetra- 

 ceros Schmarda 5 both from near New South Wales; and also Cruci- 

 fera websteri Benedict ° and Spirobranchus giganteus (Pallas) Morch 7 

 from the Gulf of Mexico. 



Fossil operculate Serpulas are rare. Among these may be men- 

 tioned the English Eocene species Serpula crassa Sowerby 8 (pi. 10, 

 fig. 11), and the Maryland Upper Cretaceous form Ornataporta mary- 

 landica Gardner. 9 The former has a calcareous operculum and a 

 three-sided tube, which is usually attached along one side to some 

 foreign object. Gabb has described some serpuloid tubes with a 

 triangular cross section, Paliurus triangularis Gabb 10 , from the Upper 

 Cretaceous at Vincentown, New Jersey. Gabb's species has no 

 known operculum, but its triangular tubes are somewhat analogous to 

 those of Sowerby's Eocene species. There are specimens of Serpula 

 Tteptagona 1X with opercula from the Barton Beds of the Eocene of 

 England in the British Museum. 



*d'Orbigny, A., Paleontologie Francaise, Terrains Crfitacgs, vol. 4, 1860, p. 214, pi. 555, figs. 4-7. 

 » Douville\ H., Mem. Socifite GGologique de France, Mem. no. 6, p. 50, pi. 7, figs. 4-7, 9-12, 14, 15. 



* Nicholson and Lydekker, Manual of Paleontology, 1889, p. 471, fig. 333a. 



s Schmarda, Ludwig, K., Neue wirbellose Thiere, 1861, p. 30, pi. 21, fig. 179, Leipzig. 



• Benedict, J. E. ( Proc. U. S. Nat. Mas., vol. 9, 1886, p. 550, pi. 21, figs. 24, 25. 

 » Idem, p. 551, pi. 23, figs. 38-42; pi. 24, figs. 43-47. 



» Agassiz, L., German edition of James Sowerby's Mineral Conchology, 1814, 1842, p. 52, pi. 30. 



8 Gardner, J. A., Maryland Geological Survey, Upper Cretaceous volume, 1916, p. 74S, pi. 47, figs. 16-l v . 



m Gabb, W. M., Proc! Acad. Nat. Sci. Philadelphia, 1876, p. 324, pi. 17, figs. 11-13. 



H Guide to the Fossil Invertebrate Animals in the British Museum, ed. 2, London, 1911, p. 79. 



