part 4] CAMBRIAN HORIZONS OF COMLET. 359 



Lapworthella, gen. nov. 



Diagnosis. — Small, tapering, annulated shells of circular or 

 sub-polygonal section, consisting of two layers, the inner one of 

 medium thickness, the outer very thin and chitinous. Annulations 

 formed by pronounced raised ridges encircle the tube, and divide 

 it into sub-equal parts. 



Type-species — Lapworthella nigra, sp. nov. 



Localities and horizon. — Lower Cambrian, near the 

 summit. Comley and Neve's Castle, both in Shropshire. 



The genus appears to be intermediate between Hyolithus 

 {Orthotheca) and Salterella, with certain resemblances to 

 Tentaculites. 



From Orthotheca it is distinguished by the character of the 

 encircling ridges, which are quite different from striae of growth. 



The resemblance to Tentaculites consists in the form and 

 disposition of the same encircling ridges. 



The relations to Salterella are much closer. In size, curvature 

 of shell, and frequent circularity of aperture the two genera have 

 much in common. The differences consist in the structure of the 

 shell and the form of the annulating ridges. 



The generic characters of Salterella are thus given by Billings : 



' small, slender, elongate-conical tubes, consisting- of several hollow cones 

 placed one within another, the last forming the chamber of habitation of the 

 animal. The cross-section of the tube is circular or sub-triangular, and they 

 are either straight or gently curved, the surface is concentrically or longi- 

 tudinally striated.' (1861, vol. i, p. 17.) 



In his description of the type-species Salterella rugosa, Billings 

 states that the annulations are formed by the projecting edges 

 of the successive cones, and Dr. Walcott's figures of the species l 

 show this structure very clearly. 



Other species referred to Salterella are (1) S. pulchella 

 Billings, 3 (2) S. curvata Shaler & Foerste, 3 and (3) Serpulites 

 maccullochi Salter. 4 



In the first the structure of the tube has a tripartite arrange- 

 ment ; in S. curvata it is stated to be thick, but no indication is 

 given of the shell-structure; in Seipitlites maccullochi the tube 

 appears to be very thick, but its structure is not described. 

 Billings suggests (op. jam cit.), however, that Salterella rugosa 

 ''must be closely allied to S. maccullochi, ' and his generic reference 

 for that species has been generally adopted. 



In the absence of any detailed study of the shell-structure of the 

 two last-named species, it may be left an open question whether 

 they should continue to be referred to the genus Salterella. 



1 1890, pi. lxxix, fig. 4. 



2 1861, p. 18. Walcott's figures of 8. pulchella (1890, pi. lxxix, figs. 5, 

 5 <i 5 e) suggest that more than one species may be represented. 



:i Shaler & Foerste, 1888, p. 34. 4 1859, p. 381. 



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