412 WHITMAN. [Vol. IV. 



Length at rest, 5-6 cm. ; width, 2.6 cm. 



Length in extension, 8.5 cm. ; width, 1.8 cm. 



Head, 4 mm. wide, scarcely marked off from the body, obtusely 

 pointed in extension, rounded or truncated at rest. 



Body, ovate-elliptical in contraction, emarginate posteriorly, 

 very thin, showing two rows of very low, smoothly rounded, meta- 

 meric protuberances on the dorsal surface, and between these 

 similar, but scattered, non-metameric protuberances. 



Disc, 9 mm. in diameter, circular, often largely covered by the 

 body. 



Annuli, 66 between the eyes and the anus, counting four 

 double rings (i, 2, 64, 65) as single rings. 



Somites, XXVI in front of the anus, XXXIII in all. 



Buccal annuli =$X.h. and 6th, united for about the middle 

 third of the ventral side, distinct towards the margins of this 

 side. 



Post-buccals = 7th and 8th, completely united below. 



Eyes, 2, rather obscure, and in contact at the anterior edge 

 of the first ring. In the young the eyes are conspicuous and 

 quite distinct, although nearly or quite contiguous. 



Mouth, in front of the centre of the flat oral sucker. 



Genital pores. — Male orifice in the loth somite, between 

 24th and 25th rings ; female orifice in the nth somite, between 

 26th and 27th rings. 



Testes = ?>vii pairs in 12th to 17th somites. 



Amis, behind the 66th ring, between this and a postanal 

 rudiment, representing probably a remnant of one or two rings. 



The annuli of the head. — In front of the eyes I was unable 

 to discover any distinct rings. In another species, C. chelydrce, 

 from Wisconsin, there are three narrow rings in front of the 

 eyes ; and the first is marked by the usual metameric sense- 

 organs. Although no metameric sense-organs were recognized 

 in front of the eyes in C. plana, the correspondence of other 

 metameric characters in the two species is sufficiently close to 

 enable me to identify the ocular rings as equivalents. The pre- 

 ocular part of the head is, therefore, probably equivalent to the 

 first somite of C. chelydrce, and is so numbered in Fig. i. The 

 ocular ring is double, representing the ist and 2d rings of the 

 second somite, so incompletely divided that the evidence of 

 duplicity is seen mainly in the relative width of the ring. 



