ART. 33 A NEW MEROSTOME CRUSTACEAN — RESSER 3 



The eyes are ovate or crescentic, pointed obliquely inward, sit- 

 uated not quite one-third the length of the cephalothorax behind the 

 anterior margin, and separated from each other by about the same 

 distance as they lie from the outer margin. As the eye lobes are 

 exfoliated their original convexity and surface can not be determined. 



Abdomen. — The dorsal side of the abdomen shows eight flat un- 

 grooved segments. The anterior segment appears to be straight, 

 although it is broken away on the right side and covered by the 

 rotated cephalon on the left, so that one can not be sure of all details 

 relating to its shape and size. Each segment back of the first 

 increases the angularity of its outer pleural portions to the middle 

 axial part, until in the eighth segment the lateral thirds of the 

 pleurae are bent back at an angle of 37°. The third segment appears 

 to be the longest and bears a short spine on the middle of the axis, 

 near its posterior edge. 



The extremities of the segments are rounded in front but sharply 

 angular at the rear. An axis of considerable width is very faintly 

 outlined, more by a slight flattening in the slope of the pleurae than 

 by an actual dorsal furrow. 



Pygidium. — The body terminates with a broad pygidial shield 

 bearing a strong telson spine. Its frontal margin is angulated to 

 fit the last thoracic segment, but the lateral and rear margins are 

 curved, forming an ovate shield. The strong spine arises on the 

 axis a little forward of the center and extends upward and backward 

 and may have exceeded the pygidium in length. At any rate it 

 must have projected beyond the rear margin. 



Surface. — The cephalothorax is covered by fairly coarse pustules. 

 These are particularly strong over what was the higher portion, 

 diminish in size toward the posterior margin, and become much 

 .smaller on the rim. Small pustules are rather evenly distributed 

 on the thoracic segments. The rear segments and pygidium seem 

 to be nearly or quite smooth. 



Measurements. — Length of animal, 57 mm.; width of cephalo- 

 thorax, 37.5 mm.; length of cephalothorax, 22.4 mm.; distance of 

 eyes apart, 14.5 mm.; length of genal spine, about 5 mm.; length of 

 thorax, 25 mm.; length of third segment, 31 mm.; length of pygid- 

 ium, 9.6 mm. ; width of pygidium, 15 mm. 



Compa')^ons. — Comparison must first be made with AgJasf/s 

 eatoni, to which Beckwithia is apparently most closely related, at 

 least as far as the characters in the cephalothorax are concerned. 

 Beckwithia agrees with Aglaspis in its pustulose test and the size of 

 the eyes, but differs in the wider spacing of the eyes and the absence 

 of a " glabella " or median lobe defined by a dorsal furrow. 



In general the abdominal segments agree in shape and relative 

 size, but Beckwithia practically or altogether lacks an axis, and has 

 eight instead of seven .segments anterior to the telson. In the telson 



