i2U CONTRIBUTION TO 



P E N T R E M I T E S G O DO N I , De France, Rowley. 



Plati-: 3G. Fi(;s. 18, 19, 20, 21, 22, 23, 24, 25. 



Figure 18 exhibits the worn ventral surface of a very ilat specimen, per 

 haps Dr. Hambach's /-*, (fhh/'cr/'atus. The spiracles that usually reach the sur- 

 face as four rounded openings are here shown to be eight paired holes. In well 

 preserved (perfect) specimens where the spiracular openings are free of rock 

 material, the knife-blade-like partition wall may be seen just within the spira- 

 cle, separating it into two canals. The least weathering develops both canals 

 as is shown in the figure. 



Figure 19 is an end view of an abnormal specimen in which the fifth ambu- 

 lacrum is ^^ anting, its place being occupied by an elongate, protuberant plate of 

 radial length, a single broad deltoid filling the space above. There are three 

 spiracles, and a rather large anal opening opposite the abortive fifth ambulac- 

 rum. 



Another specimen in our hands, larger, but of like abnormit}'', has a simple 

 spiracle, not unlike the other two, opposite the wanting ambulacrum, the anal 

 opening of usual size opposite a normal deltoid plate. 



Kaskaskia group, near Bowling Green, Ky. Collection of Mr. G. K. 

 Greene. 



Figare 20 is a small Godoni with ambulacra of different lengths, due to an 

 injury and subsequent growth. 



The specimen is considerably flattened on one side, where the ambulacrum 

 is much less than half the length of the two normal ones and of less width. The 

 two adjacent ambulacra are also shortened and somewhat distorted. 



Figure 21 is a specimen quite normal in outline but having one ambulac- 

 rum doubled two-thirds of the distance up from its distal extremity ; rather, 

 having a ridge inserted along the lancet plate as in the illustration. This ridge 

 is ribbed along its sides as ambulacral areas are and pierced along the top by 

 pores, showing plainly the doubled character of the ambulacrum. 



Specimens with a ridge the entire length of the ambulacrum are occasion- 

 ally found and the presence of the ridge can be explained by supposing two 

 ambulacra to be contiguous (an abnormity) and the later tendency of the blas- 

 toid in growth to become normal, pushing the two fields into the space of one, 

 by doubling upward the inner halves of each field into a longitudinal elevation. 

 For an illustration see figure 37. 



Both 20 and 21 are from the Kaskaskia group, of Bowling Green, Ky., and 

 the property of G. K. Greene. 



Figure 22 is a basal view of- a specimen, normal in the relative widths of the 

 ambulacral and inter-ambulacral fields, but with one of the latter filled by an 



