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



(Similar to Tetrapylonium quadrangular e, PI. 49, fig. 15), but without a sagittal girdle and with 

 stronger lateral spines.) 



Dimensions. Medullary shell 0'06 long, 0'04 broad ; cortical shell 018 long, 01 broad ; gates 

 0-007 high, 0-01 broad. 



Habitat. North Atlantic, Canary Islands, Station 353, surface. 



13. Tetrapyle quadrigata, n. sp. 



Cortical ehell thorny, with four brush-like groups of radial spines on the four diagonal corners 

 of the lateral plane, opposite in pairs in diagonal axes. Lateral girdle nearly square, somewhat 

 broader than long. Four gates kidney-shaped, twice as broad as high. On each half wing of the 

 transverse girdle five to six longitudinal rows of irregular, roundish pores. 



Dimensions. Medullary shell 0'06 long, 0'04 broad ; cortical shell 014 long, 015 broad ; 

 gates~0'03 high, 0'07 broad. 



Habitat. Pacific, central area, Station 270, surface. 



14. Tetrapyle octacantha, J. Miiller. 



Tetrapyle octacantha, J. Miiller, 1858, AbhandL d. k. Akad. d. Wiss. Berlin, p. 33, Taf. ii. 



figs. 1-6. 



Tetrapyle octacantha, Haeckel, 1862, Monogr. d. Eadiol., p. 435. 

 Tetrapyle octacantha, E. Hertwig, 1879, Organismus d. Eadiol., p. 52, Taf. iv. fig. 7. Taf. vi. 



figs. 2, 5, 5a. 



Cortical shell thorny, with eight long and thin, cylindrical radial spines, lying in two crossed 

 diagonal planes, opposite in pairs. These eight characteristic diagonal spines (or " angular spines ") 

 are the same as in Amplvipyle octoceros and many other Pylonida, and arise as prolongations of the 

 proximal edges of the four gates (or of the lateral wings on the eight points, where they are 

 intersected by the edges of the lateral ring). This cosmopolitan, widely distributed and very 

 variable species was a long time the only known species of all the Pylonida, and very accurately 

 first described (1858) by Johannes Mtiller, afterwards (1879) by It Hertwig. But in the descrip- 

 tions of these authors also some different species (such as the following) may be confounded with 

 the true typical Tetrapyle octacantha. The four gates of this species are transverse-elliptical 

 or almost triangular, nearly twice as broad as high. 



Dimensions. Length of the medullary shell - 04, breadth 0'03 ; length of the cortical shell 

 018, breadth 013 ; height of the gates 005, breadth 0'08. 



Habitat. Cosmopolitan ; very common in all warmer seas, Mediterranean, Atlantic, Indian, 

 Pacific, surface. 



15. Tetrapyle cladacantha, n. sp. 



Cortical shell thorny, with eight strong ramified radial spines, lying opposite in pairs in two 

 crossed diagonal planes, as in the preceding species. It differs from this by the peculiar ramifica- 

 tion of the eight spines, which bear two to eight simple or furcate lateral branches arising under 



