LIVING BRACHIOPODA. 337 



In a short paper in the American journal of science and arts in 1870, I first figured 

 the appearance of the oscillatory and sliding movements of the dorsal valves in Glottidia, 

 though Carl Semper ('62, '64) had described this feature eight years before. Blochmann, 

 who has recognized this mobility of the dorsal shell, was prepared to understand the 

 functions of the oblique muscles, and his nomenclature is so simple and so apt that I have 

 adopted his names in this memoir. There is but little to add to what Blochmaun has 

 given of the musculature of L. anat'ma, and that is, that the anterior occlusor muscle 

 should be recognized as containing two elements, at least, if not two distinct muscles, to 

 which the names that he has applied to similar muscles in Dlscinixca lamellosa should be 

 given, namely : occlusor anterior 1 and 2. He certainly shows the two elements in his 

 figures, but calls them simply occlusor anterior. In L. lepidula, these two muscles vary 

 in the appearance of the musciilar bundles at their points of attachment and they vary in 

 their color also (47: 6) . I did not observe the separation of these muscles in Glottidia, on 

 account of the opacity of the shell, but there is no doubt of their separation. 



It remains for me to describe the muscles of Glottidia and of L. lepidula and to 

 point out certain differences between them. In Glottidia, the oblique muscles are more 

 delicate than in L. lepidula. The terminations of the muscles in Glottidia at their points 

 of attachment vary slightly in color; the obliquus interims is greenish, the obliquus 

 medius is white, while the obliquus exteruus is silvery in appearance. The obliquus 

 medius has its dorsal attachment posterior, to that of the obliquus interims, while in L. 

 lepiditla, it is anterior to that muscle. Furthermore, in Glottidia the obliquus medius 

 passes inside of the obliquus interims, whereas in L. fi'/iii/n/tt it passes outside that muscle 

 (48:1, Glottidia; 2, L. lepidula). The points of attachment to the ventral shell appear 

 the same in both instances, except that in L. lep'uhila they are much nearer the posterior 

 portion of the shell, as in L. anat'ma. In L. leptdnla, the points of attachment of these 

 muscles show different features in color and in the nature of the tabulated appearance, as 

 shown in the figures (48 : 6, 8) . In L. lej>!iht/<i, the dorsal attachment of the lateralis 

 muscle presents features of such a character that at first I was inclined to believe that 

 they slid back and forth to a limited extent. The dorsal terminations of these muscles 

 present an appearance as if a thickened aponeurosis stood between them and that the 

 muscles were attached to this and not to the dorsal shell. Vogt ('45) and Bloehmaun 

 represent their appearance correctly. In Glottidia, however, they appeared to me to be 

 attached to the shell. In L. Icplduln, when the animal is in action, this region varies 

 greatly, as may be seen by comparing 47 : 5 and <>. In a contracted attitude of the 

 lateralis (47: 5), the oesophagus is drawn toward the stomach so as to be partly tele- 

 scoped within it, and the anterior portion of the stomach appears like two horns, only a 

 small portion of the oesophagus showing between the posterior face of the lateralis and 



