330 EDWARD S. MORSE ON 



clusters vary in the different species. In L. anathia, the posterior clusters are not so 

 prominent as in L. hjAdula and Glottidia. The lateral setae are very short, while the 

 setae of the anterior clusters are very long, the setae rapidly increasing in length from 

 the outside, and ending on the inner side of the cluster with the longest setae. The 

 middle setae of the median cluster are about half the length of the longest setae of the 

 anterior cluster, the setae becoming shorter on each side in such proportion as to form a 

 rounded outline for the cluster (40: 16). In L. lepidula (40: 6) the median cluster does 

 not assume the rounded outline seen in that of L. anatina ; it forms a pointed cluster and 

 the cluster is as long as, if not longer than, the anterior cluster, and this difference may 

 be related to the tube-forming function of the setae already described and figured 

 (40: 12) . The anterior clusters have their longest setae in the middle of the cluster and 

 not on their inner sides as in L. anatina. The clusters in Glottidia are very much like 

 those of L. lepidula, except that the median cluster is much shorter than the anterior 

 clusters. These various clusters both in Glottidia and L. lepidula are very prominent and 

 sharply defined. 



In Glottidia, the minute longitudinal markings of the setae remind one of the ruled 

 gratings for spectroscopic work, and it is this feature which causes the clear steel-gray 

 appearance and at times an iridescence when the setae are swinging back and forth. 



The transverse markings of an ordinary seta number 158, and these are separated 

 from one another the width of the seta. In L. lepidtda, the setae are colored a light 

 brown within the pallium, and this color extends some distance beyond the edge of the 

 shell, as shown in 44 : 1. 



After watching Glottidia and L. lepidula in their activities, at one time crawling 

 slowly over the sand with the setae swinging in rhythmical motion, or when half buried 

 in the sand, with the lateral setae standing at right angles to the edge of the shell and 

 forming the side partitions already described, and, in the case of L. lepidtda, forming the 

 setal tubes, one is prepared to understand the varied functions of the complex system of 

 muscle fibres which endow the borders of the pallium as depicted by Blochmann (:01). 

 In the young of Discinisca stella the anterior setae are nearly three times as long as the 

 diameter of the shell ; the length of the setae diminishes rapidly toward the posterior end 

 where they are very short (61 : 3) . In the mature D. stella, the setae are quite short and 

 crowded together, though they are slightly longer in front than those springing from the 

 posterior border. The setae in D. stella vary greatly in character; some have a brush 

 of minute hairs, others have setellae between the joints which are more widely separated 

 than those of Lingula, and in others still the setellae are extremely minute (44: 3) . The 

 setae are densely covered with various forms of minute growth. On the setae of Lino-ula 

 and Glottidia, no trace of foreign growth is seen, as their functional activity prevents any 



