159 



18. Vermicularia. — A tubular, free univalve, commencing 

 spirally, and continued more or less contorted ; the sides 

 entire, and the opening simple and round. Recent and 

 fossil.— PI. iii. fig. 18. 



The spiral commencement o? vermicularia is not marked 

 in the figure, it having been more desirable to show the form 

 in which this shell is generally found as a fossil. Indeed, 

 they occur so frequently in this form, as to give reason for 

 supposing either that the straight vermicularia forms a dis- 

 tinct species, or that, the spiral commencement being as- 

 sumed as a generic distinction, another genus should be 

 formed for the reception of the straight ones. Perhaps 

 some of the smaller fossil vermicular shells, resembling 

 those in the preceding figure, may be found to belong rather 

 to vermilia^ Lam. 



19. Serpula. — A tubular, adherent univalve, variously 

 twisted and grouped ; sometimes divided by entire septa. 

 Recent and fossil. — PI. iii. fig. 19. 



The protean character of the fossil shells of this genus 

 is very remarkable, they imitating the forms of the shells of 

 several other genera. 



20. — Conns, — A turbinated, convoluted, and reversedly 

 conical univalve ; the aperture long, narrow, toothless, and 

 not contracted at its base. Recent and fossil. — PI. iii. 

 fig. 22. 



21. Cyprcea. — An ovate and vaulted univalve; spire 

 small, and nearly covered over ; the opening narrow, the 

 length of the shell ; the margins involuted and toothed on 

 each side. Recent and fossil. — PI. iii. fig. 23. 



22. Ovula. — An obovate univalve, tumid in the middle, 

 and more or less elongated ; the opening the length of the 

 shell, with a channel at each end ; with no teeth on the left 

 side. Recent. — PI. iii. fig. 24. 



23. Bulla. — A univalve of a roundish oval form, the 

 spire not projecting ; the opening the length of the shell, 



