NO. 2164. REVISION OP ROTATORIAN OENERA—HARRING. 551 



cave. The width of the body is four-fifths the length of the dorsal 

 plate. The cross-section of the body is a shallow segment of a 

 circle. Its depth is one-third the length of the lorica. 



The anterior margin is very wide, more than one-third the length 

 of the dorsal plate. The dorsal sinus is very shallow and broadly 

 U-shaped. Its depth is one-fourth of the width. The ventral sinus 

 is V-shaped, with nearly straight sides diverging approximately at 

 a right angle, and slightly rounded posteriorly. Its depth is a Httle 

 more than half the width. Both the dorsal and the ventral plate 

 have a stippled collar. 



The foot groove is short, measuring but one-fourth the length of 

 the lorica from the base to the points where the sides of the groove 

 meet the posterior edge of the lorica. Its outline is trapezoid, trun- 

 cate anteriorly, and with widely divergent sides. Posteriorly its 

 width is one-third the length of the body. 



The foot is one-third the length of the body. Its three joints are 

 of nearly equal length. The toes are one-third the length of the 

 lorica, parallel-sided for about one-third of their length and then 

 taper abruptly to slender, nearly cyhndrical points about half the 

 entire length of the toe. At the base the toes are coalescent for 

 about one-fourth of their length, and consequently inseparable, so 

 that their movements are those of a single toe, as in the genus Mono- 

 styla. 



Total length, 145 fx; length of lorica, 102 n; width, 80 fi, width of 

 anterior margin, 36 fx; depth of dorsal sinus, 9 n, of ventral sinus, 

 20 n; length of foot groove to junction of sides and edges of ventral 

 plate, 24 n^ to posterior angle of lorica, 30 //, posterior width, 30-33 

 fx; length of foot, 30 fx, of last foot joint, 12 n; length of toes, 35 n, 

 of basal ankylosis, 8 fx; depth of body, 32 /x. 



Type.— Cat. No. 16830, U.S.N.M., from Ice House Pond, St. Paul 

 Island, Alaska. This collection was made by Dr. G. H. Parker, of 

 Harvard University, while acting as a member of the commission for 

 the investigation of the Alaskan fur seals, appointed by the Secretary 

 of Commerce in 1914. St. Paul Island is the largest and northern- 

 most island of the Pribilof group in Bering Sea ; the distance from the 

 mainland of Alaska is about 300 miles, from the Aleutian chain of 

 islands about 200 miles. 



This species is interesting on account of the sidelight it affords on 

 the generic significance of the single toe in Monostyla, as opposed to 

 the two toes of Lecane (= Cathy pna). We have here what is in every 

 other respect a typical Lepadella, possessing aU the structural pecu- 

 harities of its congeners, and yet having developed what is to all 

 intents and purposes a single toe, as in Monostyla. It is a fair infer- 

 ence that the generic value of the single toe of Monostyla is but slight; 

 this is also corroborated by the otherwise identical, or rather parallel, 

 structure of Lecane and Monostyla, even in minute details. 



