EURYPTERUS SHALES OF THE SHAWANGUNK MOUNTAINS 305, 



The addition of segments with growth may be regarded as a nor- 

 mal procedure in these Eurypterids as it is known to be in Limulus- 

 and the trilobites. Other ontogenetic variations will be referred, 

 to under the accounts to be given of the various species recognized. 



Eurypterus maria nov. - 



Plate 1, figures 1-4; plate 2, figures 1-7; plate 3, figures 1-7 



The general form of the largest observed individuals of this 

 species [pi. I, fig. 3; pi. 2, fig. 2] is elongate and slender 

 with very little abdominal expansion and no lobation of the seg- 

 ments. In these ephebic conditions the head is somewhat elongate,, 

 regularly rounded in front and with subparallel lateral margins.. 

 The eyes are crescentic, subcentral, as far asunder as the inner 

 margin of each is from the margin of the shield. 



The ocellar lobe is well defined at an early stage. A specimen. 

 63 mm long without the telson, apparently mature, has 11 segments, 

 but a break across the body leaves room enough for a 12th. The 

 width of the base of the head is 15 mm and this is but very slightly 

 less than the greatest expansion of the abdomen. Little trace of 

 surface sculpture is visible on any of the parts. 



Immature phases. The smallest individual that can be referred 

 to the species has an actual length of 5 mm [pi. 2, fig. 1] and pos- 

 sesses seven relatively broad segments tapering without expansion 

 backwards. Although this specimen is not complete, at the extremity 

 it has tapered so rapidly that there is little place for anything addi- 

 tional but the telson. Only suggestions of structural features are 

 to be seen on the head. On plate 1, figure 1, is a more complete 

 animal, 5.5 mm in length with 11 segments and the telson. .Here 

 again are only suggestions of structure on the head, but very note- 

 worthy is the marked contraction of the postabdomen bringing out 

 strongly the scorpioid abdomen which now seems indicative of a 

 nepionic condition both in ontogeny and phylogeny. Probably 

 certain well known large merostomes like Eurypterus Scor- 

 pio i d e s and species of Eusarcus in which this abdominal expan- 

 sion is pronounced at maturity, are to be interpreted as arrested in 

 respect to such development. In the chapter on the Merostomata 

 in Zittel-Eastman's Textbook of Paleontology I introduced figures 

 of immature examples of Eurypterus r e m i p e s [p. 676, 

 fig. 1420, 1421], the smallest individuals of any Eurypterid known 

 at that time, wherein this abdominal contraction and expansion is 

 strongly pronounced and in the smaller of the two there is also a 

 very marked paucity of abdominal segments. This abdominal con- 



