REPTILIAN AGE. JURASSIC PERIOD. 12'? 



the section of all our larger specimens is more nearly circular, and they appear 

 never to possess the broad, shallow groove represented by D'Orbigny's figui-es, on 

 the ventral side, near the apex, Some individuals have on that part of the shell a 

 linear groove, but it seems never to widen upwards as represented in B. Panderi- 

 anus. There is also on some of our larger specimens a sUght carina near the apex 

 of the dorsal side (Fig. \g, PI. V), not represented by D'Orbigny's figures, nor 

 mentioned in his description. 



Along with these large specimens we find several smaller ones, having a propor- 

 tionally more slender form, and a more nearly central axial line. Some of these 

 also have a quite distinct, though narrow, ventral groove (Figs, d, e, /, PI. V), while 

 their transverse section varies from subcircular to oblong-oval. These, we suspect, 

 belong to a distinct species, but, without better and more extensive collections for 

 comparison, we have not been quite able to satisfy ourselves they may not be 

 younger individuals of the more robust form. These two varieties appear to bear 

 exactly the same relations that the large and small specimens of B. Panderianus 

 figured by D'Orbigny do to each other. 



Locality and position. — Southwest base of the Black HUls, associated with Eumir 

 Gratis curta, and other Jurassic fossils. (Type, No. 195.) 



SuBKiNGDOM AETICULATA. 

 Class AWIVULATA. 



Order TuMcola. 

 Family SERPULID^. 



Enveloping tube more or less calcareous, or membranaceous. 



Animal vermiform, rounded or somewhat compressed; segments short. 

 Head lobe soldered to the oral segment, and not distinct in the adult. 

 Oral segment with a pencil of setas on each side, and generally provided 

 with a collar. Mouth directed forward, without a proboscis, situated 

 between the bases of the branchial plumes. Branchi^ two, one on each 

 side, either semicircular, circular, or spirally coiled ; consisting of a basal 

 membrane, from the anterior margin of which the threads arise, either in 

 a single or double row. Set^e simple and of two kinds, capillary or hooked. 



The recent genera included in this family are Anisomelus, Sabella, Eriographis, 

 Protula, Serpula, Spirorhis, Filograna, and Fahricia. 



i The fossil forms described under the names Hamtdus, Spiridcea (or Rotidarid), 

 Gydogyra, Serpulites, Trachyderma, Sec, probably also belong to this famUy. 



Genus SERPULA, Linn^us. 



Synon.—Serpula, Likn^us, Syst. Nat. 10th ed. 1758, 786 ; ib. 12th ed. 1767.— BRno. Encyo. Meth. I, 1792, xiv.— 



Lamarck, Syst. An. 1801, 325.— Blainv. Diet. Sci. Nat. XL VIII, 1827, 549, &o. 

 Etym. — Serpoj to creep. 

 Examp. — Serpula vermicularis, Lin. 



