ATLANT. DEEP-SEA EXPED. 1910. VOL. III). 



PTEROPODA. 



23 



5) The longitudinal striae of the radula-teeth are also 

 less conspicuous. 



Geographical distribution. This species is by 

 Meisenheimer (1905,1906) recorded as being widely distri- 

 buted within the warmer currents of the Atlantic Ocean 

 (the Mediterranean inclusive), only occasionally finding its 

 way into the cooler waters of northern (59° 26' N. Boas 

 1886) or southern (42° 18' S. Meisenheimer 1905) latitudes. 

 — It has been found, although not frequently, also in 

 the Indo-Australian and Pacific oceans. 



During the "Michael Sars" expedition Clio cuspidata 

 was taken at many stations, especially in the eastern part 

 of the Northern Atlantic, usually in the water-layer between 

 100 and 250 metres, as shown in the table, the table also 

 shows that its occurrence at the Northern latitude recorded 

 by Boas is no isolated phenomenon, for it was taken at 

 two stations (98, 101) near this latitude. 



Clio (Euclio) pyramidata Linne. 

 PI. Ill, fig. 22-23, 27. 



No pteropod is better known and more often de- 

 scribed and figured than this species. It is, therefore, a 

 curious fact that a very obvious asymmetry of its mantle 

 has, so far as I have been able to ascertain, escaped 

 attention. 



The right side of the mantle-margin is in all 

 well preserved specimens much more fully developed than 

 the left side, and protrudes like a broad 

 folded membrane visible on the dorsal as 

 well as on the ventral side of the animal 

 (fig. 22 — 23 m). Inside of this membrane is 

 found the little lobe-like gilHalready known 

 in Limacina helicoides, Clio faicala and C. 

 cuspidata (fig. 27 g). 



The ventral lobe of the foot is, in 

 comparison with the above-named species, 

 still further reduced, forming only a narrow 

 rounded lobe during rest covering the mouth 

 and the bases of the wing-like lateral lobes. 



The transversely striated mantle- 

 gland of Clio falcata and Clio cuspidata is 

 in this species replaced by the well-known 

 semicircular shield-like gland, whose border 

 is formed by a broad finely striped U-shaped 

 ribbon. 



Geographical distribution. Clio 

 pyramidata is one of the commonest repre- 

 sentatives of thecosomatous pteropods in all 

 oceans, — a widely distributed inhabitant of 

 warm and temperate regions. 



f^^ffO 



Fig. 22. Varieties of Clio pyramidata.' 

 A angusta, B lata, C convexa. 



The eurythermal character of this species was con- 

 firmed during the "Michael Sars" expedition, it having 

 been taken at no less than 23 stations scattered over the 

 North Atlantic, and from various depths. A glance at the 

 table shows, however, that it is not equally distributed, 

 but at some places occurs in dense swarms, as at stations 

 23, 42, 82, 84. In some of these swarms (indicated by 



var. angusta, © var. lata, $ transitional forms. 



Fig. 23. Clio pyramidata. 



