674 SYSTEMATIC PALEONTOLOGY 



intervening between the rows of strong spines are each occupied by a row 

 of very much smaller, laterally compressed spines whose bases are more 

 or less connected. 



" There is considerable variation shown in the surface markings of 

 different individuals of this species, and the extremes might be taken as 

 the representatives of distinct species or even of distinct subgenera. In 

 its typical form, as seen in the Tinton beds, the species exhibits clearly the 

 characteristics of the subgenus Criocardium, the rows of spines rising 

 from the interspaces betwen the radiating costa3 of the shell. In some 

 specimens the bases of the larger spines or nodes are confluent and appear 

 to entirely fill the interspace occupied by them, so that the two bounding 

 costae with the row of spines together seem to constitute a single broad rib 

 crowned with a row of strong nodes. At the same time the rows of secon- 

 dary nodes are sometimes confluent at their bases and form a continuous 

 secondary rib, perhaps nodose on top, and about equaling in height and 

 size the primary costas, so that there seem to be three costae of nearly equal 

 size in the broad interspace between the rows of large nodes and their 

 included bounding costae. In the extreme development of the rows of 

 secondary nodes their bases are confluent and they increase in size and 

 height so as to occupy the whole of the interspaces, obliterating entirely 

 the primary costae, so that the surface of the shell is apparently marked by 

 radiating rows of tubercles which apparently do not rise from interspaces 

 between costae, but directly from the surface, each third row being much 

 larger and stronger than the two intervening ones. 



" It is possible that larger collections of more perfectly preserved 

 material than is now available would show that more than one species has 

 been included under this head, but so far as can be determined from 

 present collections, all these forms seem to run together. The typical 

 form of the species, however, is that in which the nodes rise distinctly from 

 the interspaces, showing the characters clearly of the subgenus Crio- 

 cardium, and which has been recognized only in the Tinton beds. 



" In its somewhat elongate and slender form, the species in the form 

 of internal casts somewhat resembles the casts of C. spillmani and they 

 have sometimes been so identified. It does not grow so large as that 



