148 



g.) Ynrious modes of ornaiiientatioii, such as tubercles, 

 rings, and spinous processes, occur, though frequently the 

 stem is (]uite plain. (Fig. 21),/,/.) A remarkable example 

 of a closely-coiled stem from the Demissa bed is illustrated 

 in Fig. 21), /. It was coiled in a single plane, resembling 

 much a non-involute cephalopod shell. The coiling probably 

 occurred dui-ing th(- life of the animal, the stem having been 

 severed tVom the root by some accident. 



Roots. — These are occasionally met with, attached to the 

 shells of brachio|)ods. on coi-als, and on other objects of sup- 

 ])ort. ( Mg. 21). ni-<>: see, also. Fig. '.'>().) 



Class Ax.\eli[»a. Mac Lkav. 



Tlie annelids, or typical worms, are soft-bodied, marine, fresh-water, 

 or terrestrial animals, whose remains can seldom be preserved in a fossil 

 state. It is only the tube-building order {Tuhicola) which leaves any 

 satisfactory remains. In these the tube is either a calcareous secretion of 

 the animal, or it is composed of agglutinated sand and other foreign 

 particles, being, in each case, wholly external. The peculiar bodies 

 known as Conodonts are supposed to be the jaws of annelids. Worm 

 burrows are often preserved by sand or mud infiltration, a cast of the 

 burrow appearing in the strata. 



Note. — The anatomy of recent worms is treated of at length in most 

 text-books of zoology, to which the student is referred for further 

 information. 



The literature on Vonodontx is scattered. Pander's Monographie der 

 Fossileu-Fische des Silurischen Systems des Russisch-Baltischen Gouv- 

 ernements (1851), treats of them at length, they being there considered 

 as fish teeth. A paper by Zittel and Rohen entitled " Ueber Conodonten," 

 and published in the Sitzu ngi^bericM der Bayruclien Akademie der Wissen- 

 Kcluiften, Bd. XVI., 1886, discusses them in detail, and brings out their 

 annelid affinities. Hinde's paper is quoted below. 



TUBES. 



Genus SPIRORP.IS. Lamakk. 



[Ety. : A. spiral whorl] 

 (1801: Syst. An. .mns Vert., p. :«6,) 



Minute, s{)ii-fdly-coiled calcareous tubes, wdiich are 

 cemented to some foreign substance by one side. Surface 

 smooth or ornamented with concentric stri^p or annulations. 



I 



