32 PROCEEDINGS OE THE NATION AIj MUSEUM vou 72 



POLYGNATHUS CONCENTRICUS Ulrich and Sassier. 1926 



Plate 11, figs. 5-7 



1926. Polygnathus concctitricns Ulrtch and Basslek, Proc. U. S. Nat. Mus., 

 vol 68, p. 47, pi. 8, figs. 6, 7. 



The plate is roughly triangular, having three Avell-defined lobes. 

 The rounded lateral lobes gradually disappear into the sides of the 

 sharp-pointed anterior lobe by means of a shallow, curving indenta- 

 tion. The plate is slightly depressed toward the posterior end but 

 elevated in the anterior lobe. The median ridge, which is low but 

 sharp in the posterior end, extends the entire length of the plate and 

 in the anterior lobe becomes broad, being produced be3^ond the plate 

 hj a carina bearing several round, compressed denticles. Both the 

 median ridge and the carina are somewhat sinuous in their courses. 

 Short tubercules are concentrically arranged in the lobes. In the 

 anterior lobe, where they cross the median ridge, they are so closely 

 spaced as to appear as continuous lines. Compared with Polygnathus 

 trilohahiSy this species differs in its more finely marked basal portion 

 and in the extension of the median ridge to the anterior extremity. 



Ples7atypes.-—Cat. No. 11457, U.S.N.M. 



POLYGNATHUS RHOMBOIDEUS Ulrich and Bassler 



Plate 11, figs. 11, 12 



1926. Polyfrnuthus rhombotdcus Ulrich and Bassler, Proc. U. S. Nat. Mus., 

 vol. 68, p. 46, pi. 7, fig. 6. 



Plate rhomboidal in shape. Posterior lobe long and narrow. 

 Lateral lobes slightly broader and somewhat rounded. The median 

 ridge which extends the length of the plate is extended beyond the 

 plate by a short, narrow carina, bearing several denticles, varying in 

 shape and size. These denticles are extensions of those borne on the 

 median ridge. In the anterior end of the plate the ridge is traversed 

 by tubercules concentrically arranged but terminating abruptly at 

 the ill-defined base of the ridge. Parallel rows of denticles extend 

 from the anterior lobe to the origin of the carina, where they turn 

 at a sharp angle and terminate in the margin of the lateral lobes. 



The rhomboidal shape, less conspicuous transverse ribs, fewer 

 rows of tubercules, and their more longitudinal arrangement, dis- 

 tinguish this species from its allies such as Polygnathus concent licus. 



Plesiotypes.— Cat. No. 11456, U.S.N.M. 



POLYGNATHUS PENNATULOIDEA, new species 

 Plate 11, fig. 14 



This species is somewhat similar to Polygtudhus penmitulus 

 Ulrich and Bassler. The high median ridge is surmounted by 



