E. W. Shuler — New Ordovician Eurypterid. 553 



tal one being the larger. The alveolar processes in all the seg- 

 ments have a distinct serial arrangement along a median line. 

 The pronounced flattening of the bristles or spines gave a 

 much enlarged paddle-like surface to the whole endognathite. 



The anterior margins of the segments show a smooth arcuate 

 curve without dentition. The joints show the expected thick- 

 ening around the articulating surfaces. 



The second appendage, tig. 3, also shows three segments. 

 These are shorter and more robust than the joints of the 

 appendage just described. They do not show spines, though 

 this may be due to the conditions of preservation. The frag- 

 ment is probably a part of the first endognathite. The meas- 

 urements, beginning with the proximal joint, are as follows : 

 length, 8*™, 7 mrr , 7 ram ; the corresponding widths are : 4 mm , 2 , 5 rnm , 



Oram 



A part of the telson spine with the impression of the last 

 two abdominal segments is shown in fig. 3. The posterior 

 segment has a length of 16 mm ; the second has a length, esti- 

 mated from the curvature of the mould, of 19 mm . A number 

 of measurements of Stylonurus and other Eurypterida showed 

 a rather constant ratio between the length of these two seg- 

 ments and the total length of the individual. This ratio was 

 approximately one to eight. While no special stress is laid on 

 such a ratio, it is interesting that this would indicate that the 

 complete specimen was 280 mm long (about eleven inches). 



Fig. 6 represents what appears to be a segment of one of 

 the walking or balancing legs, typical of Stylonurus. It has 

 a length of 30 mm , but this probably does not represent the 

 total length of the segment. The width at the proximal end is 

 4 mm ; at the distal end, 2'5 mm . Fig. 5 shows a fragment of an 

 unidentified limb. 



The fragment of the carapace shows the mould of one of the 

 compound eyes, two depressions questionably identified as 

 ocelli, and the impression of a rough tubercular surface. The 

 supposed ocelli lie well back behind the compound eye and the 

 general appearance is more that of Eusarcus than Stylonurus. 

 The state of preservation is, however, such as to preclude a 

 definite identification or exact description. Fig. 2 shows an 

 enlarged view (X2) of the tubercular moulds. 



This merostome has been provisionally referred to Ctenojp- 

 terus, a sub-genus of Stylonurus, on account of the long flat- 

 tened segments of the endognathite ; the lack of serrations on 

 the segments such as is found in Eurypterus ; the presence of 

 the long joint belonging probably to the walking leg or bal- 

 ancer, characteristic of Stylonurus ; and the long broadened 

 spines or bristles which are especially characteristic of the sub- 

 genus Ctenopterus. It has been given the specific name alveo- 



