Characters o/'Lingula anatina. 11 



branches of the primary vessels that pass backward external 

 to the ante-latero-parietals, — on entering the present compart- 

 ments they separate a little, and pass on, anastomosing here 

 and there, to the posterior part of the valves. Both on their 

 inner and outer sides spring a number of offshoots : the outer 

 pass direct to the pallial margins ; and the inner (n), some curving 

 backward, and others forward, pass to the post-latero-parietals. 

 The main branches define, as it were, the outer boundary of 

 each pleuroccele ; while the inner offshoots are often sufficiently 

 prominent to give an irregularly puckered character to its 

 upper and under (pallial) surfaces. 



The next structure to be described may be not inappro- 

 priately introduced under the present head, though it belongs 

 equally to the brachioccele. 



Both pallial lobes have a slightly raised flattened band (u) 

 from an eighth to a quarter of an inch in width, the widest 

 part being in front : it runs round the pallial margins, from 

 which its outer edge (w) is distant about one sixteenth of an 

 inch. The attachment of the band is strongest at its inner 

 edge (which nearly corresponds with the line of vascular con- 

 striction, v) : the outer edge, somewhat thickened or corded, is so 

 slightly attached that there is no difficulty, by inserting a fine 

 blade underneath, in separating it from the mantle ; while 

 further inward the attachment is even slighter, permitting the 

 band to be raised in its entire width except along its inner 

 edge. Numerous long setae are well known to characterize 

 the pallial margins of the Palliobranchs. In Lingula these 

 parts (x) have their basal portion, about one third of their length, 

 imbedded in the band : they pass nearly to its inner edge, and 

 lie so close to each other, side by side, as to form a divisional 

 plane or an upper layer in it. On raising the upper layer, 

 the cause of its slight attachment is at once perceived ; for the 

 seta? are tied down to the mantle only along the base of the 

 corded margin of the band. 



Although the setal band, as it may be termed, runs along 

 the pallial margins in their entire extent, the course of the 

 seta? in the ventral valve is interrupted in one part — that is, in 

 the region of the pedicle (figs. 1 & 4) : there is no interruption in 

 the opposite part of the dorsal valve*. The band in both 

 valves gradually thickens on approaching the hinge ; at which 

 part it is puckered, and somewhat reduced in width (fig. 4, u), 

 the incrassation giving it a prominent appearance. In the 

 ventral valve, where the seta? are interrupted, the attachment 

 of the outer edge is discontinued (fig. 3, u), the band being 



* In Distinct lamellosa the setse are not interrupted in either valve- 



