1002 THE VOYAGE OF H.M.S. CHALLENGER. 



4. Tym/paniscus tripodiscus, n. sp. (PL 94, fig. 7). 



Basal ring of about the same size as the mitral riug, with three large and stout divergent feet 

 (two lateral and one caudal). Sagittal ring stout, broader than the two spiny subsagittal rings ; 

 the upper part of the latter bears two ascending arches, which are united with the large apical horn 

 arising from the apex of the sagittal ring. Six columella nearly vertical, slightly curved on the 

 outside ; their lateral edges armed with numerous simple or forked spines. 



Dimensions. — Breadth of the shell O'l, total length 0'12. 



Habitat. — Central Pacific, Station 265, depth 2900 fathoms. 



5. Tympaniscus qtiadrupes, n. sp. (PL 94, fig. 4). 



Basal ring larger than the mitral ring, with four short vertical three-sided pyramidal feet of 

 equal size (two lateral and two sagittal) ; the feet are three-sided pyramidal, with finely denticulate 

 median edges, and bear at the base a horizontal thorny spur. Sagittal ring at the apex with a very 

 large cross-shaped horn, bearing two horizontal thorny lateral branches ; the horn is supported by 

 an anterior and a posterior arch. Six columella; strongly curved and dentate. 



Dimensions. — Breadth of the shell 015, length 012. 



Habitat. — South Pacific, Station 298, depth 2225 fathoms. 



6. Tympaniscus fibula, HaeckeL 



Ceratospijris fibula, Ehrenherg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xx. 

 fig. 3. 



Basal ring of about the same size as the mitral ring, with six large conical descending feet; 

 these are prolongations of the six columellae, nearly of the same length, slightly divergent, and bear 

 at the base a strong horizontal spur. The six columellae are strongly curved, spiny, and bear above 

 small arches, which are united with the apical horn of the sagittal ring. 



Dimensions. — Breadth of the shell 0'09, height 0'05 ; total height 0'09. 



Habitat. — Fossil in Barbados. 



7. Tympaniscus dodecaster-, n. sp. 



Basal ring of the same size as the mitral ring, with six very large and six alternating smaller, 

 slightly divergent, curved feet, about as long as the shell ; the larger are the basal prolongations 

 of the six curved, thorny columellije. Mitral ring spiny, not overgrown with arches, as in the 

 similar preceding species. 



Dimensions. — Length of the shell 0"08, breadth 012. 



Habitat. — Tropical Atlantic, Station 347, depth 2250 fathoms. 



