DESCRIPTION OF NEW SPECIES. K'x 



appearance. This is move clearly shown in figure 14. which is a side 

 view of the knob-like Astrae-form tubercle of the outer surface when un- 

 abraded. On plate 1 figure 1 represents a dermal plate with two raised 

 tubercles and numerous small Astrse-form tubercles, and figure 2 is the 

 outer surface of a supposed lateral plate. Figures 3 and 4, plate 4, repre- 

 sent the outer surfaces of partially abraded plates* 



SUB-ORDEK < JROSSOITERYGEA. 



Family Holoptychidida. . 



ERIPTYCHIUS AMKKK AXIS, X. -1'. 



This species is hased entirely upon the separated scales. It is not im- 

 probable that several species are represented in the material, the better 

 preserved portion of which is illustrated in plate 4. figures 5 toll. Figures 

 ") and 6 are broad scales, each showing the bearing surface or facet of the 

 next anterior scale and the ornamented exterior surface. The latter has 

 numerous elevated longitudinal lines upon it, Figure 7 is a fragment ol 

 a scale with irregular stellate surface ornamentation, and figure 8 another 

 fragment of a scale of the same type. Figure 9 is a phase of surface 

 ornamentation somewhat like that of figure 8, and figure 10 is an inter- 

 mediate phase of ornamentation between that of figure 7 and those of 

 figures 5 and 6. Figure 11 represents the interior of a narrow scale that 

 shows the poriferous inner surface and. where broken away, the base of 

 the elevated longitudinal lines of the outer surface. 



Plate •"> illustrates the microscopic structure of the remains of both the 

 species discriminated. 



♦ During the fall of 1891, a portion of the head earapae< "I A straspis desiderata was found in a 



very fine grained calcareous sandstone. It measures 73mm in length bj " im in widthatthe 



posterior margin and 40mm toward the front. It is formed by the union of a great number of small 

 plates, such as are illustrated "ii plate :;. figures 10-14. A median ridge formed "t elevated, tuber- 

 culated plates extends from the posterior margin 13mm toward the front, very much ;i- in tin- he id 

 shield of Thyestes verrucosus, Eichwald, from the Silurian rocks of the island of Oesel, Russia A 



Miml ii' ridge occurs on each si. I.- that extends forward 28i from the posterior margin ; they are 



13 i from tlir mediap ridge at tin- base and 9i from ii at their anterior termination A marginal 



ridge occurs on each side of tin' specimen that i- continuous with tin- margin so far as (In- latter 

 is preserved. Directly in front of the median ridge a group of 12 plates having elevated cen 

 are clustered around ■■> central plate that rises at the center above tin- others. On each side of this 

 cluster "i plates a larger plate (4 x 6mm) occurs that has six elevated tuberculated points on it. 

 interior to this there is a plate with two points and another with three. Over other portions 

 the carapace tin- plates have usually only a single elevation near the center. The small Astra- 

 form tubercles occur on all the plates. "I he form "t tin- portion of the carapace preserved ami it~ 

 appearance suggests tin- cephalaspian fishes "i the Silurian of Russia, while tin- separate plates and 



i : , ., form tubercles foreshadow the Asterolepidse of the lower Devonian.— March, i - 



