1356 THE VOYAGE OF H.M.S. CHALLENGER. 



conical, curved wings of half tlie length, arising from its lower third (immediately above the girdle). 

 Abdomen inversely campanulate. Pores subregular, circular, of equal size. 



Dimensions. — Length of the three joints, a 0-04, h 007, c 0-04 ; breadth, a 0-03, b 0-07, c 0-05. 



Eahitat. — Central Pacific, Station 272, depth 2600 fathoms. 



6. Lithornithium hirundo, Ehrenberg. 



Litliocampe hirundo, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 65. 

 Lithornithium hirundo, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 53. 



Shell nearly ovate, with two deep strictures. Length of the three joints = 2:6:4, breadth = 

 2:7:5. Cephalis hemispherical, with an oblique, conical horn of twice the length. Thorax 

 hemispherical, with three long, angular, little divergent wings of twice the length, which are S-shaped, 

 cui-ved, and arise from its lower third, immediately above the girdle. Abdomen inversely conical. 

 Pores irregular, roundish, of different sizes. In the figure of Ehrenberg the abdomen is broken off; 

 in a specimen from Caltanisetta, with somewhat shorter and broader wings, I found it complete. 



Dimensions. — Length of the three joints, a 0-02, h 0-06, c 0-04; breadth, a 0-02, h 0-07, c 0-05. 



Habitat. — Fossil in Tertiary rocks of the Mediterranean (^Egina, Greece ; Caltanisetta, Sicily). 



Genus 596. Sethornithnim,^ Haeckel, 1881, Prodromus, p. 436. 



Definition. — T h e o p e r i d a (vel Tricyrtida triradiata clausa) with three Latticed 

 lateral wincrs on the thorax. 



The genus Sethornithium differs from the preceding Lithornithium, its ancestral 

 form, only in the fenestration of the three thoracic wings, and bears therefore to it the 

 same relation that Dictyoceras exhibits to Pterocorys. 



1. Sethornithium dictyopterum, n. sp. 



Shell ovate, with two slight strictures. Length of the three joints = 2:4:3, breadth = 1:5:4. 

 Cephalis ovate, with a pyramidal horn of twice the length. From the middle part of the thorax 

 arise three broad, triangular, latticed wings of about the same length, the distal end of each of which 

 is curved downwards. Abdomen inversely conical. Pores regular, circular. (Similar to Lithornithium 

 fringilla, PI. 67, fig. 2, but with much larger wings, which in the greater part are fenestrated.) 



Dinmisions. — Length of the three joints, a 0-04, 6 O'OS, c O'OB ; breadth, a 0-02, b Ol, e 0-08. 



Rahitat.— Central Pacific, Station 271, depth 2425 fathoms. 



1 Sethornithium ^httticed bird; aiiSa, oouidot. 



