358 MARIONEIXA 



times markedly so. When well-developed, these organs consist of highly 

 refractive elements, both external and internal, which are very striking in 

 their appearance. To a considerable extent these supplements can be pro- 

 truded and withdrawn. When protruded they are very prominent. When 

 withdrawn they may leave the ventral contour comparatively even; and 

 yet, even when withdrawn, they are hardly less conspicuous than when 

 protruded, owing to their highly refractive character. The most striking 

 internal elements are two in number to each supplement, extending, one 

 forward and the other backward, and may appropriately be termed "levers'* 

 These levers are somewhat finger-shaped pieces of cutinized material that 

 serve for the attachment of muscles. They usually taper but little, and 

 their internal extremities are invariably blunt. The two levers of a given 

 supplement are usually practically equal in size. When the supplement 

 is at rest, the levers lie near the ventral side of the body and parallel to it. 

 In such circumstances the exterior portion of the organ protrudes only slightly; 

 but when the free inner ends of the levers are drawn inward so that they lie 

 at an angle with the ventral surface, sometimes as great an angle as forty- 

 five degrees, the external portions of the supplements are protruded. The 

 external portion of each organ has the form of a laterally compressed cup, 

 or trough, whose profile is exteriorly flat, or more often slightly concave, 

 and interiorly more or less semi-circular. While the depth of the organ may 

 sometimes equal its width, often it is less, and sometimes only one-half or 

 one-third as great. Those species showing the maximum development of 

 the supplementary organs present cases where the depth of the organ is 

 one-fourth as great as the corresponding diameter of the body. In one species 

 the supplementary organs are asymmetrical, the anterior lever or anchor 

 having become vestigial, and the anterior portion of the cup or trough having 

 diminished relatively in size, so that the contour of the longitudinal section 

 of the organ is triangular rather than semicircular. By means of a duct 

 each supplementary organ is connected internally and forward with a large 

 glandular cell, as in Bolbella. 



Setae on the male. Just in front of the anus on the male there are usually 

 to be found a few minute setae, either ventral or subventral in position. 

 They are very short and very inconspicuous. There may be a single one 

 at the anus; more often there are one or two subventral ones on each side 

 Occasionally there are two rows extending to near the posterior supplement. 

 These setae are arcuate, acute, and when two are present on each side of 

 the anus, one of the pair is usually located immediately behind the other 

 and is of smaller size. No other papillae or setae have been observed on 

 the tail end of the male. There is no bursa. 



Habitat. The genus Marionella has hitherto been supposed to be of rather 

 small size. It is in reality large, and is widespread in the various oceans. 

 While the individuals of a given species may not be numerous, or very wide- 

 spread, the number of specific forms observed is yearly augmenting. The 

 two sexes are about equally common. 



The genus is most nearly related structurally to Bolbella, Symplocostoma, 

 Thoonchus and Catalaimus. 



Marionella spectabilis (Marion) is still retained as the type species. 



