108 POTERIOCRINID^ EXTRACRINUS. 



The rays in adult animals amounted to nearly the same number as in the typical 

 species, but the tentacula are attached in a different manner. In the E. Briareus they 

 articulate on to projections designed for their support, but in this species they fit into 

 notches, or shallow depressions in the ray joints. The tentacula are closely set to the 

 end of the rays. The ray joints are not so rotund as in the E. Briareus, and their mode 

 of articulation is somewhat different, as maybe seen on reference to PI. 13, figures g, h. 



The plated integument which covers the abdominal pouch closely resemble that of 

 the typical species, but in the E. lepidotus there was also a plated membrane extending 

 between each group of the lower rays. The plates which protected this integument are 

 in some specimens still found in the same position they occupied during the life of the 

 animal, and impart a very beautiful appearance to the fossil skeleton. The membrane 

 alluded to was attached laterally to the secondary rays, and was eapabable of consider- 

 able extension, and in consequence of its pliancy did not interfere with the movement 

 of the rays. The plates are highly polished, and are arranged in a regular definite form, 

 and bear some resemblance to scales, from which circumstance we derived the specific 

 name. From the manner in which the plates covering this portion of the membrane 

 adhere laterally to the lower portion of the rays, it is evident that the outer sides of the 

 leading rays to which they are attached, are devoid of tentacula, as their points of adhe- 

 sion are occupied by the scale-like plates, which are arranged in regular series in a 

 (Mrcular form around hexagonal, or heptagonal central pieces, and which arrangement 

 produces a beautiful floriform appearance. 



The column is formed of alternate thick and thin joints, which externally are less 

 pentagonal than in the E. Briareus, but the pentapetalous crenated markings on the 

 articulating surfaces of the joints are nearly as pentangular as those on the articulations 

 of that species. 



Near the upper part of the column a majority of the thicker articulations are each 

 furnished with five round auxiliary side aims. These claspers are not placed in a line 

 directly over each other as in the preceding species, but they are disposed alternately 

 right and left in the retiring angles of the column, and thus form a double series. Several 

 consecutive joints above each point of attachment of the side arms are grooved or fuiTowed 

 perpendicularly to the axis of the column, so as to form a narrow channel in which the 

 delicate claspers might lie when the aninial desired to present the least possible resistance 

 to the passing current. The manner in which the claspers are inserted into and articu- 

 late to the column is represented in the enlarged portion of a column, PI. 13. fig. 1, e. 



We have not in this instance retained Miller's specific name because several species of 

 true Pentacrinus possess the same external form of column, therefore since the discovery 



