1889.] NATURAL SCIENCES OF PHILADELPHIA. 1 45 



plates convex, rounded hexagonal ; side arm plates convex, about 

 three times as high as broad, not meeting above or below, bearing a 

 single small arm spine rather more than halfway up the side of the 

 arm ; on some of the arm plates there are one or more extremely rudi- 

 mentary papillae; mouth tentacle pores opening into the mouth slit, and 

 having six; tentacle scales on the inner side and five on the outer; 

 five tentacle scales on the inner side of the sixth arm plate and one 

 tentacle scale on the outer side ; farther out the ten- 

 tacle scales on the outer side of the tentacle pores 

 disappear altogether ; papilla? of an arm comb about 

 \ < -»5^^l k "/ seventeen in number, squarish flat and touching each 

 <S^A^k^5 other and borne by a semicircular plate about four 

 Fig. 7. times as long as broad; under arm plates rather 



convex, irregularly hexagonal, longer than broad ; about nine mouth 

 papillae in each mouth angle, those at the side of the angle small 

 flattened, three rather larger pointed ones at the apex. Diameter of 

 disk 9 mm. ; length of arms 17 mm. 

 £J^ Color of the two dried specimens, dull straw. 



Thjs form approximates more or less to many of the 

 Fig. 8. species of this prolific genus but may be distinguished by 

 its large ovate mouth shields, and the following combination of 

 characters: — the possession of a single arm spine, the shape of the 

 upper and lower arm plates, and the arrangement of the plates 

 covering the disk. 



11 



