PLATE 2, 3, 4-. 
Fig. 1. The stipe of the even Entrochite, as commonly 
found in Derbyshire*, a. a. small angular dints or cavities, 
in which the arms were inserted in the original. 
This fossil has generally been considered as the remains 
of the Isis Entrocha of Linne ; but if the characters of that 
animal are correctly given in the last edition of the Systeyna 
Natiira (p. 3794<. n. 4.) the prototype of our Entrochite is 
certainly a distinct species. The arms or branches in the 
Isis Entrocha arc particularly described as being vertlcillate, 
dichotomous, and continuous or not jointed; in the present 
* All the Derbyshire Entvochit<e I have yet collected agree in the follow- 
Jng particulars. 
The stem is columnar, jointed, perforated longitudinally through the cen« 
tre, and in most instances furnished with lateral arms or branches. 
The disks, or intertial surfaces of the joints by which they are united to 
one another, are flat and radiated with close slender strire, drawn from the 
centre to the margin : the radiations of each joint tally with those of the 
next with which they are in contact; and, thus joined, the extremities of 
the stria form minutely crenulated lines, encircling the stem, and externally 
marking out the several commissures. On the inside, the joints are pully- 
shaped, or like a small wheel surrounded by a deep, angular groove or 
/urrow. When the joints are entire the grooves are filled and hidden by the 
ambits, which collectively constitute the external surface of the stem. 
The central perforation of the joints is produced by the total or partial 
removal of five tubular filiform bodies, closely surrounding a sixth, of a 
similar shape and structure. These are bound together, as it were, by smaU, 
transverse, circular, equidistant, plate-like parts, (vide fig. 5, 6, 8) which 
divide with the commissures of the stem, but are rarely visible, except in 
sueJt specimens as have lost more or less of the exterior coverings. 
