1004 THE VOYAGE OF H.M.S. CHALLENGER. 



Subgenus 2. Tympanomma, Haeckel. 



Definition. — Shell with sixteen gates (eight median gates, paired on both sides of 

 the sagittal ring, and eight lateral gates, j^aired on both sides of the frontal ring). 

 The four lateral gates of the two preceding species (subgenus Tympanura) are bisected 

 in Tympanomma by the lateral parts of an incomplete equatorial ring. 



3. Tympanidium binoctonum, n. sp. (PI. 94, fig. 18). 



Shell with sixteen gates ; the four lateral gates double, bisected by the lateral parts of 

 an incomplete equatorial ring. Basal gates nearly rectangular, of the same breadth as the 

 pentagonal mitral gates, but twice as long. Equatorial outline of the shell (seen in fig. 18 from the 

 apical pole) octagonal. All rods of the shell thin, smooth. 



Dimensions. — Transverse axis of the shell 0-1, sagittal axis 0"06. 



Sabitat. — Western Tropical Pacific, Station 225, depth 4475 fathoms. 



4. Tympanidium barhadense, Haeckel. 



"Hollow cyliuder," &c., Bury, 1862, Polycystins of Barbados, pi. xvi. fig. 1. 



Shell with sixteen gates ; the four lateral gates double, bisected by an incomplete equatorial 

 ring. Basal gates kidney-shaped, of the same breadth as the circular mitral gates, but twice 

 as long. Equatorial outline of the shell elliptical. All rods of the shell thin, smooth. 



Dimensions. — Transverse axis of the shell 012, sagittal axis 0'08. 



Habitat. — Fossil in South Naparima, Trinidad, Barbados. 



5. Tympanidium staurocircum, n. sp. 



Shell with sixteen gates ; the four lateral gates double, bisected by an incomplete equatorial 

 ring. Basal and mitral gates of the shell of about equal size, roundish. Equatorial outline of 

 the shell xiolin-shaped, with a sagittal constriction. All rods of the shell armed with short 

 irregular spines. 



Dimensions. — Transverse axis of the shell 012, sagittal axis 0-06. 



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



Subfamily 2. Paratympanida, Haeckel, 1881, Prodromus, p. 447. 



Definition. — T y m p a n i d a with two fenestrated horizontal rings, which are 

 connected by a variable number of vertical rods or columellas. The shell therefore 

 becomes more completely latticed than in the other Tympanida, and approaches that of 

 the S p 5^ r i d e a. 



