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



four to five turnings. The sixth chamber twice as broad as the trizonal medullary shell. Tores 

 irregular, roundish. Surface of the shell thorny. 



Dimensions. Breadth of the spiral cortical shell 0'27, height 0'25 ; breadth of the medullary 

 shell 0-05, height 0'06. 



Habitat. Pacific, central area, Station 265, depth 2900 fathoms. 



Family XXXI. PHORTICIDA, Haeckel (PL 49, figs. 10, 11\ 



Phorticida, Haeckel, 1881, Prodromus, p. 464. 



Definition. L a r c o i d e a with quite irregular monothalamous shell, representing 

 irregular modifications of an original lentelliptical latticed shell ; the irregular cortical 

 shell encloses a regular or subregular, lentelliptical or trizonal medullary shell. 



The family Phorticida comprises a small number of Larcoidea in which a 

 subregular, trizonal, lentelliptical medullary shell is enclosed by an irregular simple or 

 spongy cortical shell. The lattice-work of the latter is sometimes simple and com- 

 plete, at other times incomplete, with open gates (as in the Pylonida), sometimes also 

 spongy. Its form is always more or less irregular, roundish, often dimply or 

 tuberous ; different from most other Larcoidea. 



The medullary shell is constantly a regular or subregular Larnacilla-shell, composed 

 of three elliptical latticed girdles of different sizes, perpendicular one to another. This 

 leaves no doubt that the Phorticida are true Larcoidea. The connection of it with 

 the cortical shell is rarely effected by radial beams, commonly by two opposite latticed 

 wings, which are identical with the lateral halves of the transverse girdle in the Pylonida 

 diplozonaria (Amphipyle, Tetrapyle). Often also between this transverse and a 

 second (lateral) girdle there remain large open gates, so that the affinity between these 

 Phorticida and the Pylonida cannot be doubted. In other cases these gates become 

 closed, so that they more nearly approach the Larnacida. From both families they differ 

 by the irregularity of the papillate or tuberous cortical shell. The network is more 

 or less irregular, its surface often thorny, but never covered with symmetrically disposed 

 radial spines. 



The central capsule is lentelliptical, encloses the medullary shell, and is enveloped 

 by the cortical shell, as in the nearly allied Pylonida and Larnacida, of which the 

 Phorticida may be regarded as irregular aberrant forms. 



Synopsis of the Genera of Phorticida. 



Cortical shell simply latticed, . .313. Phorticium. 



Cortical shell spongy, . . 3U - SpongophorHs. 



