﻿schuchert] sn.ruic ami dkvonic cystidea 209 



or discrete-pectinirhombs having interior calcareous folds. At least 

 one pectinirhomb is always situated on the basal opposite to the anus 

 [plate []. Anus laterally above the widest basal. Column and 

 roots well developed; the uppermost segments alternating with col- 

 lared pieces." (Jaekel, p. [94.) 



Explanation of Some of the Terms Used in the Present Work 



Plate formula. — The system of numbering the thecal plates in the 

 following descriptions and diagrams is that of Bather {Treatise on 

 Zoo!., in, 1900). These numbers were probably first applied by 

 Edward Forbes as early as 1848. Hall, in 1852, used a similar nota- 

 tion in describing- Callocystites. The diagram of the latter genus 

 given on page 244 has the full number of plates, and the student 

 should familiarize himself with it. 



Theca. — The cup containing the viscera and composed of a vari- 

 able number of thecal plates. The mouth is at the end opposite to 

 that attached to the column or stem. From the mouth radiate the 

 ambulacra. Just beneath the mouth is the small porous plate known 

 as the madreporite, which is connected with the stone canal. Usually 

 in contact with the madreporite is a very minute pore, the hydropore 

 or parietal pore, and in well-preserved specimens this is closed by a 

 pyramid of plates. Still further beneath the mouth is the large 

 aperture of the anus closed by the anal pyramid. Besides these parts 

 the theca always has 3 pectinirhombs situated on 6 plates, or on 

 plates 1 and 5, 12 and 18, and 14 and 15. 



Ambulacra. — The recumbent or prostrate arms upon the theca. 

 The lower biserial pieces are the ambulacrals and the roofing pieces 

 over the radial grooves are the ambulacralia. On and between the 

 ambulacrals are the ' fingers ' or brachiolcs. 



Pectinirhomb. — The parallel dichopores arranged across a suture 

 between 2 plates, and combined into a rhomb. When the two halves 

 are not separated medially by walls they are here referred to as 

 pectinirhombs, but when the two halves are distinctly separated and 

 each part is surrounded by a waif, they are termed discrete-pectini- 

 rhombs. 



Family Callocystid^e Bernard 



This family is defined by Jaekel as follows : 



Regularia with the " theca closed to the mouth, plates in the circles 

 in complete numbers. Ambulacra with paired ambulacralia and 

 paramhulacralia, projected radially over the theca and provided with 

 numerous brachioles (fingers). Anus of medium size, generally sur- 



