742 ORDER HYPOTRICHA. 



Fam. I. LITONOTIDiE, S. K. 



Animalcules free-swimming, soft and flexible, lanceolate or elongate, 

 having a narrower and often highly elastic neck-like anterior prolongation ; 

 the entire ventral surface flat, finely ciliate throughout ; the dorsal surface 

 smooth and glabrous, mostly convex ; the oral aperture ventral, a series of 

 larger pre-oral cilia mostly developed in advance of the oral aperture ; 

 pharynx unarmed ; trichocysts usually abundant. 



The Litonotids, including at present the single genus Litonotus, represents one 

 of the lowest groups of the Hypotricha. But for the absence of cilia on the dorsal 

 surface, which up to a verj- recent date were presumed to exist, the several species 

 closely resemble such simply organized Holotricha as Amphileptus and Loxophyllum, 

 and to which two genera they have, indeed, been previously relegated. In no other 

 Hypotricha have as yet the existence of trichocysts been demonstrated, and in no 

 other members of this order does the cuticular investment possess so great an 

 amount of elasticity. 



Genus I. LITONOTUS, Wrzesniowski. 



Animalcules free-swimming, highly flexible, more or less elastic, of 

 elongate outline, the anterior extremity attenuate and neck-like, often 

 exceedingly prolonged ; the ventral surface flattened and ciliate throughout, 

 the dorsal aspect smooth and convex ; oral aperture situated at the base of 

 the neck-like prolongation, close to the left-hand border ; the cortical layer 

 usually enclosing trichocysts ; endoplasts two in number, ovate or spherical, 

 closely approximated and united by a cord-like commissure. 



The generic title of Litonotus has been instituted by Wrzesniowski* for the 

 reception of those animalcules previously referred to the genus Loxophyllum, but 

 which he has demonstrated by more precise investigation to be ciliate only on their 

 lower or ventral surface. This last-named structural characteristic has necessitated 

 the transfer of these t>'pes from the Holotrichous to the Hypotrichous order of the 

 Ciliata ; at the same time they may be regarded as constituting a bond of union 

 between the two, their affinity with Loxophyllum and Amphileptus on the one hand, 

 and through Loxodes to the more tj'pical Hypotricha on the other, being self- 

 evident. 



Litonotus Wrzesniowskii, S. K. Pl. XLH. Figs. 12 and 13. 



Body elongate, linear-lanceolate, the posterior extremity pointed, de- 

 pressed, and tail-like, produced anteriorly into a long, flat, very slender, 

 highly flexible and contractile neck-like portion, which is slightly dilated at 

 the distal end, and whose length equals that of about three-fifths of the entire 

 body ; oral aperture situated at the base and to the left-hand side of the 

 neck-like prolongation ; ventral surface of the body furrowed longitudi- 

 nally, the cilia short and fine, disposed in even lines along these furrows ; 

 the cilia fringing the neck of larger size than those clothing the ventral 



* " Infusorien aus der Umgebung von Warschau," 'Zeitschrift fiir Wissenschaftliche Zoologie,' 

 Bd. XX., 1870. 



