6 3 6 



MOLLUSCOIDEA. 



cell-mouth is surrounded by a thickened border, and the species con- 

 tained in it range from the Chalk to the present day. 



The family of the Cribrilinidce comprises forms in which the poly- 

 zoary is sometimes incrusting, sometimes free and foliaceous. The 

 zocecia have their front wall more or less fissured, or traversed by 

 radiating ribs separated by intervening furrows, which may be closed 

 or perforated (fig. 482, b). The type-genus of this family is Crib- 

 rilina itself {—Lepralia in part), of which both recent and fossil 

 forms are known, the earliest of the latter appearing in the Cretaceous 

 deposits. 



The family of the Microporellidcz also includes a number of the 

 incrusting or erect types of Polyzoa which were included by older 



Fig. 482. — A, Cells of Micropora complanata (Tertiary and Recent), enlarged ; b, Cells of 

 Cribriliiia radiata (Cretaceous, Tertiary, and Recent), enlarged ; c, Cells of Microporella im- 

 pressa (Tertiary and Recent), enlarged. (After Hincks.) 



writers under the comprehensive name of Lepralia ; the essential 

 characters of the family being found in the fact that the cell-aperture 

 is more or less semicircular, with an entire lower margin, while the 

 front wall of the zocecia exhibits a semilunate or circular " special 

 pore" (fig. 482, c). The type-genus of this family is Microporella 

 itself, the species of which are Tertiary and Recent. 



The great family of the Escharidce (including under this name 

 also the Myriozoidce of Hincks) comprises forms in which the poly- 

 zoary is always completely calcareous, and may be incrusting, or 

 erect and foliaceous, or sometimes dendroid. The zooecia are with- 

 out a membranous area or raised margins, the cell-wall being entire 

 or variously punctured, but always without special pores opening 

 into the perivisceral cavity. In the Tertiary and Recent genus 

 Schizoporella (fig. 483, b) the polyzoary is sometimes incrusting, 

 sometimes free and foliaceous, and the lower lip of the cell-aperture 

 has a distinct notch or sinus, representing the median pore in the 

 Microporellidce. In the genus Hippothoa the form of the cell-mouth 

 is very similar to that seen in Schizoporella, but the zooecia are " dis- 



