430 



24 b. CyECUM (? ELEGANTISSIMUM, Var.) SeaRLES-WoODIJ. 



C. (Anellum) t. parva, graeillima, elongata, alba, subdiaphana, 

 subvitrea ; annulis subobsoletis, creberrimis, subacutis cincta, 

 seu interdum sublcevi ; septo ungulato, apice subdextrorsum 

 sito ; margine laterali subrecto : operculo ? . . . 



Test. adol. long. -046, lat. -007— '012. 



Test, adult, long. -068, lat. '008— -013. 



Hab. Teneriffe, in gravel sand, 50 fms., very rare (R. M' Andrew). 

 Mus. Brit. &c. 



= Caecum Searles-Woodii, Cpr. in M'Andr. Rep. Moll. N. E. Atl., 

 Br. Ass. 1856, p. 149. 



Twenty-three specimens were found differing from C. elegantis- 

 simum as above stated. It is annulated from a very early stage ; 

 the rings are closer (about twenty-four in the young shell), scarcely 

 sharp, and often obsolete ; the growth is scarcely tapering and very 

 slender ; and the plug is ungulate, turned somewhat to the right. 

 Whether it prove to be a dwarfed condition of C. elegantissimum, or 

 a distinct species, it is named in remembrance of the author of the 

 invaluable Monograph of the Crag Mollusca, where the plugs of 

 Caeca were first described. 



25. Cecum undatum, ? n. s. 



C. (Anellum) t. obesa, curta ; t. jun. leevi ; t. adulta annulis 

 x.-xv. acutis cincta; interstitiis concavis, undatis ; antice et 

 postice contracta, planis decollationis et aperturce ad ang. 

 circ. 115°; apertura contractu, dein paululum rejlexa, acuta ; 

 septo ungulato; apice acuto, elongato, prominent e ; margine 

 laterali recto: operculo concavo, anfr. circ. xv., sutura distincta. 



Variat t. minus obesa, annulis subobsoletis. 



Test. jun. long. '042, lat. -01. 



Test. adol. long. -067, lat. 01— -02. 



Test, adult, long. -074, lat. -021. 



Hab. Mazatlan, abundant in worm-eaten shells of Spondylus cal- 

 cifer, &c. (? Panama, 1 sp., C. B. Ad.). Mus. Brit. &c. 



Maz. Cat. p. 323 ; Brit. Ass. Rep. 1856, pi. 9. f. 4 a-o. 



Test. adol. ? = C. parvum, C. B. Ad. Pan. Shells, pp. 163, 311 : 

 " t. arcuata, gracili, vix tereti ; albida ; annulis xv. acutis, distan- 

 tibus, haud multum elevatis ; apice laterali, prominente. Long. # 065, 

 lat. -019." Sp. un. Mus. Amherst. 



At least 500 specimens have been examined of this species, in 

 almost every stage of growth ; both young and adults, to the number 

 of about fifty, containing their opercula. By this means the mode 

 and variation in growth were ascertained, and the knowledge gained 

 applied to the other species where connecting links were not ac- 

 cessible. The " monstrosum " stage, in which the tube hitherto 

 smooth and slender suddenly alters its angle of growth and diameter, 

 assuming sharp rings, is very remarkable. The posterior contrac- 



