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



The genus Spirema begins the series of the Sijiremida, or of those Lithelida in 

 which the medullary shell presents a simple latticed sphere or ellipsoid, never composed 

 of a double, trizoual or Xary(«ci7/a-shaped shell. In the present state of our knowledge 

 we cannot say whether this simple medullary shell be a primary formation, or effected 

 by secondary means, by reduction of a double Xarnac^7Za-shaped medullary shell, which 

 is constantly found in the Larcospirida. The species of this genus (as of all Lithelida) 

 are difficult to distinguish, are transformistic, and incline very much to variations and 

 abnormalities. The spiral may be simple or double. 



Subgenus 1. Spiremarium, Haeckel. 

 Definition. — Spiral convolutions of the cortical shell simple. 



1. Spirema lenteUij)sis, n. sp. 



Cortical shell lentelliptical, with smooth surface ; proportion of its three dimensive axes = 4:5:6. 

 In the median plane are \isible four perfect turnings of the simjjle spiral, the breadth of which 

 gradually increases towards the third convolution, finally decreasing ; the broadest (third) turning 

 three times as broad as the simple spherical medullary shell. 



Dimensions. — Length of the lentelliptical cortical shell 018, breadth OlS, height 0"12 ; 

 diameter of the spherical medullary shell 0'02. 



Habitat. — North Atlantic, Station 353, surface. 



2. Spirema melonia, n. sp. (PI. 49, fig. 1). 



Cortical shell nearly spherical, with smooth surface ; proportion of its three dimensive axes 

 = 1'4: 1"5 : 1'6. In the median plane are visible three perfect turnings of the simple spiral, all of 

 the same breadth as the simple spherical medullary shell ; the breadth of each convolution somewhat 

 greater at the poles of the principal than at the poles of the sagittal axis. 



Dimensions. — Length of the shell 016, breadth 0-15, height 014; medullary shell O'OIS. 



Halitat. — Pacific, central area, Station 271, surface. 



3. Spirema fiustrella, Haeckel. 



Flustrella haliomma, Ehrenberg (1861), Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, p. 293, 

 Taf. ii. fig. 6. 



Cortical shell egg-shaped, with thorny surface ; proportion of its three axes = 4:5:6. In the 

 median plane are visible three perfect turnings of the simple spiral, the first and second of about 

 the same breadth as the simple spherical medullary shell, the third suddenly increasing, and finally 

 three to four times as broad. Network of the surface irregular, with roundish pores. 



Dimensions. — Length of the sheU 0^2, breadth 017, height 014 ; medullary shell 0-013. 



Habitat. — North Atlantic, Greenland, 1000 fathoms, Ehrenberg ; Fasroe Channel, John Murray. 



