Wappinger Valley Limestones. 149 



distance along the sides ; from this point, the sides are nearly 

 straight, except at the posterior end, where there is an expan- 

 sion into a broad, rounded, well-marked annulation, whose out- 

 lines are everywhere curved. Between the ring and the main 

 body is a transverse, linear, deeply impressed furrow. There 

 is a pair of short faint furrows, together forming a V, just in 

 front of the posterior transverse furrow on each side. 



From the central point of the front edge, a broad moderately 

 deep furrow, extends a short distance backward, rapidly con- 

 tracting to a vanishing point ; it obscurely divides the anterior 

 part of the hypostoma into two lobes. There is anteriorly, a 

 narrow, rounded margin whose contour conforms to that of the 

 front edge of the principal mass. It is uncertain from the 

 partially imbedded specimens, whether or not, this margin 

 extends also along the sides. 



The thorax contains eight segments. Axis well- elevated, 

 strongly convex, rate of taper regular, about one part in six. 

 Each segment is of about the same width as the corresponding 

 pleural segment, exclusive of the free spinous portion. 



A linear furrow, deeply impressed, passing from one pos- 

 terior corner to the other, traverses each segment through its 

 central point. This furrow thus presents the shape of an arc 

 convex anteriorly. Immediately behind its central and highest 

 point there is a tubercle, or perhaps the base of a spine. All 

 that portion of each segment lying within, and posterior to the 

 furrow, presents a visible contrast to the anterior portion by 

 some slight difference in the texture of its surface, which, for 

 one thing, is a little the rougher ; in the two specimens col- 

 lected, it is also of a darker color. The pleural segments are 

 depressed convex, and extend out very nearly at right angles to 

 the central line of the axis, until the free spinous portions 

 are reached. Each of the pleurse consists of a broad, flat 

 depressed portion or furrow, flanked by narrow, well-defined 

 marginal ridges. The furrow is broad at its inner end, and 

 continues of equal width for half the distance, when it rapidly 

 draws down to a point. The posterior pleural ridge is almost 

 perfectly straight through its entire length ; the anterior ridge 

 is straight for about half its length, while it lies appressed 

 against the posterior ridge of the next segment in front ; from 

 this point it is at first gently, then rapidly recurved until it 

 meets in an acute point the posterior ridge of its own segment. 

 All the narrowing of the pleurae is thus effected from the 

 anterior side. The pleural segments are prolonged into flat, 

 acute, recurved spines, with broad contiguous bases ; their 

 length is about two-thirds that of the main segments ; their 

 inner, concave edges appear to be continuations of the posterior 

 pleural ridges. 



