are, on the OBphalon, known as ti on the thorax and pygidium as the 



plfu>,i. /i. The two longitudinal grooves dividing the entire test are the <ii-snl fur- 



. The glalwlla partakes of a segmentation siiuil.ir to that of the thorax, hut 

 incomplete, the dividing grooves rarely extending across it These grooves are the 

 lateral ylnMlar t'urr<i * and are usually in three pairs (sometimes four, and sometimes 

 wholly obscured) which are numbered l>y pairs from the anterior backward ( 

 i >f the lobes formed by these furrows the anterior, or frontal loin; I, is large and 

 unpaired; thence backward the lutt-ral lubes are n am be red to correspond with the 

 furrows, each lobe lying behind the furrow with which it corresponds numerically, 

 The posterior end of the glabella is limited by a transverse furrow, the 



itnl i/ri>i >, og, behind which lies a distinct segment or occipital ring, or; both of 

 these extend on to the cheeks of the cephalon and form a coalesced segment. 



The lateral expansions of the cephalon or the cheeks are usually divided into two 

 parts by a f,i,-!al suture, s, which extends from the posterior or lateral margin to 

 the anterior margin. The teat was readily separable along these lines after the 

 sloughing of the integument or the decomposition of the lining tissue. The outer 

 or separable portions are known as the /re* cheeks, fc, the inner portion between the 

 sutures and the dorsal furrows, as the ftted cheeks, x. In a few genera the facial 

 sutures are obscure or not developed, but where they exist the cephalon consists of 

 three plates, two free cheeks and a central intrasutuml plate to which the term 

 cranulium is here applied. The cranidium consists of the glabella, fixed cheeks and a 



ter or less portion of the occipital ring. The outer lateral margin of the cephalon 

 may lie thickened into a border, b, which meets the occipital ring at the outer posterior 

 angle of the cheek (genal angle). This angle may be obtuse, acute or produced into 

 spines of greater or less length (<jenal spines, *p). The eyes, which are present in all 

 but a few very early genera, are situated on the cheeks and are traversed by the facial 

 sutures which leave the inner portion of the eye-node (paljirbral lobe, n) on the fixed 

 cheek, and the outer, visual portion (e), or that bearing the lenses, on the free 

 cheek. 



The thorax, T, is composed of a variable number of movable, separable parts or 

 segments, sg. The axis of each bears an anterior ring which is overlapped by the 

 outer ring of that preceding, and thus forms an articulation. The groove between 

 the double axial ring of each segment is called the articulating groove. The pleur.i- 

 are frequently beveled on their anterior surface near their extremities, so that 

 adjoining segments readily slipped over one another when the animal contracted or 

 enrolled itself. The lateral parts of the segments are frequently divided transversely 

 by a pleural groove, pg. The extremities of the segment may be acute or obtuse. 



