NOTICE OF PALEONTOLOGY OF NEW YORK. 



185 



volution, are united by a loop which is produced by the extension of a 

 slender process from the band on each side, and these are united at 

 a greater or less distance from their origin. Beyond this junction the 

 parts of the loop again divide, and each one is produced in a curving 

 band which arches forward on the ventral side, and thence returning is 

 reunited to the sides of the loop at or near the junction of the parts 

 before noticed. 



These features are illustrated in the accompanying diagram ; fig. 1 

 being an oblique lateral view of the central portion of the spires of 

 Meristella arcuata^ and fig. 2 a view of the same parts from the dorsal side. 



Fig. 1. 



Fig. 2. 



In these figures, a indicates the origin of the crura; h the recurvation 

 of the lamellae, which may be as represented, or with a simple retral 

 bending without recurving upon itself in some species ; c is the continua- 

 tion of the lamellae, which at d give ofi" the processes forming the loop, 

 and these become united at e and continue simple to /, where they bifur- 

 cate and continue in the direction g, returning again to the centre, and 

 reuniting with the loop at h, or near the junction of the two parts before 

 mentioned. 



These characters of the spires and loop have been observed in the M. 

 Icevis, M. arcuata and M. princeps of the Lower Helderberg group, and in 

 the M. larrisi of the Hamilton group ; while the M. nasuta presents a 

 slight modification in the extension of the parts of the loop, which ally 

 it more nearly with Athtris. 



When compared with the spires of Athtris as shown in the figures 



already given under that genus,' as well as the illustrations of Davidson 



and other authors, the differences are obvious. The parts of the loop in 



this genus, instead of curving forward and there uniting and turning 



Cab. Nat. 24 



