532 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 51. 



rial representations of this animal. Depending as usual for generic 

 distinction upon the number of eyespots, in this case incorrectly 

 observed, Ehrenberg added a new generic name, Mdopidia, and made 

 use also of Bory de St. Vincent's Squamella, which was originally 

 proposed for Bracliionus bractea Miiller, a Euchlanis species, probably 

 E. dilatata. Dujardin reduced these three genera to one, retainmg the 

 name Le/padella; as this is the oldest available name, it has been used 

 here in preference to Metopidia, the generic designation employed 

 by Hudson and Gosse. It should be borne in mind that the types 

 are different, and Metopidia may at some future date be revived, 

 when a subdivision of the present genus becomes necessary. With 

 the comparatively small number of species now known, there is no 

 occasion for a division among such closely related forms. 



The Lepadellids are a group of uniformly small ploimate Rotatoria 

 related to the EucUanids and characterized by the peculiar structure 

 of the lorica. While without any actual division, it is convenient 

 to describe the lorica as composed of a dorsal and a ventral plate, 

 rigidly united at the edges. This also serves as a remmder of the 

 probable development of the lorica, as noted in the introduction; it 

 seems evident that the Lepadellids are descended from ancestors 

 protected only by a firm dorsal plate, the ventral integument being 

 flexible, with the suture where we now find the edge of the lorica. 

 On this assumption only is the structure of the Lepadellid lorica in 

 its present form intelligible. 



The lorica has at the anterior end an opening for the protrusion of 

 the head and on the ventral surface, some distance from the posterior 

 end, there is a perforation tlu-ough which the foot projects. The 

 outline of the lorica is usually ovate; in some species it is provided 

 with lateral spurs or wing-like extensions, giving it a rhomboid or 

 trianguloid appearance. The cross section of the body in the typical 

 group is a segment of a cu'cle, of varying height; in the Mdopidia- 

 group it is triradiate, in various degrees of development. The dorsal 

 plate has near its posterior end two openings for the lateral antennae; 

 these are indicated in the figures, but, as their position is so nearly 

 uniform in the genus, no mention has been made of them in the 

 descriptions. 



The anterior opening of the lorica is usually supplemented by a 

 dorsal sinus of moderate depth and a relatively large ventral sinus 

 is always present. To give additional room for the free movement 

 of the head the ventral plate curves downward around the anterior 

 opening. In reading the descriptions of the dorsal and ventral 

 sinus the fact that the animals are not flat must be kept in mind; 

 what is actually seen is a projection on a plane of a structure with 

 appreciable depth, as will be realized from the lateral views, and 

 the anterior points shown in the dorsal and ventral views are in 



