60 THE DEVONIAN OF MISSOURI. 



Remarks — The most remarkable thing about this crinoid are deep pits at the 

 angles of the plates. From these pits the surface rises to the middle of the plates, form- 

 ing low broad cones. Each plate is surrounded by 5 or usually 6 of the pits. Ridges 

 cross from plate to plate between the pits, and sutures are rarely apparent. The ridges, 

 pits, and cones distinguish the species from Melocrinus gregeri which has the same 

 arrangement of plates though it is a much larger form. 



Occurrence — Snyder Creek shale of Callaway County. The specimen figured is the 

 holotype from the collection of Professor R. R. Rowley. 



Melocrinus tersus Rowley 



Plate 7, figures 9 and 10 



1894. Melocrinus tersus Rowley, Am. Geologist, XIII, pp. 151-152, fig. 1. 

 1909. Melocrinus tersus Greger, Am. Jour. Sci., XXVII, p. 376. 



Rowley's description — "Calyx obconical; dome almost flat, basal plates four, three 

 of which are quadrangular, the fourth and largest pentagonal. Breadth nearly twice 

 the length, but slightly expanded; excavated for the reception of the column. 



Of the first radials, three are heptagonal and two are hexagonal; width a little 

 greater than length. Of the second radials two are heptagonal, two hexagonal, another? 

 octagonal. In the ray to the left of the anal area, the second radial? is entirely separated 

 from the first radial (a malformation) by the abutment of the lower lateral edges of 

 the large piece of the anal area and the large interradial to the left of the anal area. 

 Third radials heptagonal, supporting, on the upper sloping sides, two small secondary 

 radials. 



Interradial areas filled by from 12 to 14 pieces, the lowest one of which is almost 

 as large as the first radial and hexagonal. In two of the areas two plates rest on the 

 upper sides of the first interradial and first radial, while in one area three such plates 

 are above the first. There seem to be about ten plates in the anal interradius, but this 

 can not be well made out from the disordered condition of the radjial series to the left. 

 All of the calyx as well as the vault plates are slightly convex but without spines and 

 radiating ridges, except at the edges where short connecting ridges give a pitted character 

 to the lines of union. 



Vault pieces numerous. Base of proboscis medium, excentric. Base of the free 

 rays prominent, giving an actinocrinoid look to this beautiful species. Top stem joint 

 rather large." 



Remarks — Rowley's type is abnormal in the anal and adjoining rays. Another 

 specimen, collected from the type locality, has the following arrangement of the plates: 

 In the anal area 1, 3, 4, 5, 5; in other interrays 1, 2, 3, 4, 4; 1, 2, 3, 3, 4; 1, 2, 2, 2, 3; 

 1, 2, 3, 3, 3. Arrangement of plates in the type: Anal area 1, 2, 2, 3, 4; other interrays 

 1, 2, 2, 3, 4; 1, 2, 2, 3, 4; 1, 3, 3, 3, 4; 1, 2, 3, 4, 5. The second specimen is slightly longer 

 compared to the width than the type and the plates are strongly convex, while in the 

 type they are slightly convex. At nearly every angle between the plates a pore is present 

 in the type, but only a few pores are present in the other specimen. The ridges be- 

 tween the basals and radials are less prominent and fewer than in the type. 



A large series might show Melocrinus tersus and M. gregeri to be conspecific, though 

 spines are absent on the known specimens of the former and are prominent on the latter, 

 and the former is much smaller and less expanded at the top. Measurements of two 

 specimens of M. gregeri show height 30 and 31 mm., greatest width 31 and 34 mm., oJ 

 two specimens of M. tersus, height 20 and 22 mm., width 18 mm. 



Occurrence — Known only from location 1, Snyder Creek shale, Callaway County. 



