O-N A NEW FORM OF AGELACEINTTES. 151 



At the outer edge of the test the plates are small, closely set, and 

 probably fixed : passing inwards they increase in size, the largest 

 series defining the inner edge of the outer zone ; while those of the 

 interradial spaces are of medium size, and are pressed upwards 

 against the arms, so that their edges form margins to each of the 

 rays, doubtless due to post-mortem pressure. The imbrication of 

 the plates is from without inwards, the inner margins of the plates 

 being free. 



The nearest allies of this fossil are doubtless Lepidodiscus Lebouri, 

 Sladen,' L. cincinnatiensis, E.om.,^ and L. squamosus, Meek & 

 Worthen,^ but as detailed comparisons of these and other species, 

 as well as full references, are given by Mr. Sladen, our present 

 purpose will be best served by merely giving the chief characters 

 of our specimen, and of the three nearly-related forms, as follows: — 



Lepidodiscus squamosus. 



1. Arms 5, long, extending along margin. 



2. Arm-plates in double rows. 



3. Pyramid at one side of interradial space. 



4. No outer border seen. 



5. Diameter 1*70 inch. 



cincinnatiensis. 



1. Arms 5, long, extending along margin, 



2. Arm-plates in double rows. 



3. Pyramid near outer edge, touching end of arm. 



4. Outer border indistinct and narrow. 



5. Diameter 0*77 inch. 



Lepidodiscus Lehouri. 



1. Arms 6 [? abnormal], long, extending along margin. 



2. Arm-plates in single rows. 



3. Pyramid at one side of interradial space. 



4. An outer border. 



5. Diameter, when perfect, somewhat over 1 inch, 



Lepidodiscus. n. sp. 



1. Arms 5, short, not extending along margin. 



2. Arm-plates, in part at least, in double rows. 



3. Pyramid in middle of interradial space. 



4. A broad distinct outer border. 



5. Diameter 0*40 inch (1 centimetre). 



A comparison of the above characters shows that our new speci- 

 men diff'ers from all the others in having short arms, and the pyramid 

 in the middle of the interradial space, also in its much smaller size. 



It further differs from L. squamosus and L. cincinnatiensis in 



^ Op. et he. cit. 



2 See Geol. Surv. Ohio, vol. i. part 2, Palseont. p. 55, pi. 3. f. 6. 



3 Proc. Acad. Nat. Sci. Philad. 1868, p. 357. 

 Q.J.G.S. No. 190. M 



