144 ALEXANDROMENIA VALIDA. 



The cells of the posterior pedal gland are of comparatively^ small size, but 

 otherwise are essentially the same as those of the anterior pedal gland. As 

 usual they open by separate intercellular exits into the pedal furrow. 



In several species of Solenogastres the foot is accompanied by two longi- 

 tudinal ridges, modifications of the hj'podermis. In the present species the 

 median projection is bordered by two prominences on each side. All are of 

 essentially the same size and appearance, being thin folds of epithelium into 

 which a few muscle and connective-tissue fibres project. No blood spaces 

 occur within them and at their bases the secretion from the pedal gland finds 

 its outlet. 



The atrial cavity in the only specimen examined is of limited extent (Plate 11, 

 fig. 3), but it possesses ridges of large size that together with the cirrose area 

 presents a very characteristic appearance. The indistinct prominence, which 

 in some species accompanies the outer ridge, is not sharply defined, being recog- 

 nizable solely by the rod-like group of ganglion cells in the customary position. 

 The outer atrial ridge proper is of large size, and as a much folded, horseshoe- 

 shaped elevation surrounds the atrial cavity except posteriorly. The inner 

 fold is of inferior size and consists of two ridges which arise independently on 

 the roof and posteriorly diminish in size and gradually disappear. Their epi- 

 thelial covering consists of high slender cells with elongated subcentrally placed 

 nuclei distal to. which the cytoplasm contains quantities of light yellow pigment. 

 Internally the folds are supported by strands of connective tissue with a small 

 admixture of muscle fibres among which well-defined blood sinuses pursue their 

 course. 



The cirri arise singly from the atrial wall and are of more than ordinary 

 thickness. As usual each consists of an outgrowth of the buccal wall, composed 

 of more or less cubical cells in which the yellowish brown pigment is so abundant 

 that it usually conceals the nucleus. The cavity of each cirrus is very narrow, 

 allowing the passage of a nerve strand but not of the blood. 



The buccal cavity or pharynx, separated from the atrial cavity by a circular 

 fold (Plate 11, fig. 3), is an irregular cavity whose general appearance and rela- 

 tions are represented in Plate 21. The walls throughout are produced into 

 numerous wavy, more or less longitudinal folds, lined with a thin cuticular sheet. 

 In the middle third, which contains the radula, the folds become more distinctly 

 longitudinal, but more posteriorly they once more become very irregular. 



As in A . agassizi there are three sets of salivary glands, and as may be seen 

 in Plate 21, figs. 2, 4, in arrangement and size, they are essentially the same as 



