OBOLID^. 503 



a few large punctse were seen on the interior of one ventral valve. The shell is unusually thick 

 for its size. It has a thin outer layer and several inner layers or lamellae that are arranged very 

 much as in Lingulella acutangula (Roemer) (PI. XVII). 



A relatively large ventral valve has a length of 7 mm. and a width of about 5.5 mm. 



The cast of the area of the ventral valve shows a long area divided midway by a narrow 

 pedicle groove, and toward the lateral margins by a very narrow flexure line. The area of the 

 dorsal valve is shorter in proportion than that of the ventral valve, and also less extended on 

 the cardinal slopes. The cast of the visceral cavity (v), including the outline of the heart-shaped 

 cavity (x), is very well shown by Plate XXXVIII, figures 2a and 2b. There are no traces of a 

 median septum in the ventral valve, but in the dorsal valve it is a very narrow sharp crest on 

 the summit of the broad, strong, median ridge that extends from the area fully three-fourths of 

 the distance to the front margin; the septum appears to be confined to the anterior half of the 

 length of the ridge. 



The muscle scars are not clearly defined in either valve. The trapezoidal areas of the 

 ventral valve, where the central scars and the middle and outside laterals are usually located, 

 are present, but the individual scars can not be differentiated. In the dorsal valve the central 

 scars appear to be unusually large; they are situated on each side of the broad median ridge, and 

 crowd the parietal scar out to the main vascular sinus ; the anterior laterals are situated on each 

 side of the median septum, as shown in Plate XXXVIII, figure 2d, but they are not well defined. 

 ■ The main vascular sinuses of the veritral valve extend far forward and curve inward so 

 that they appear nearly to unite a short distance back of the anterior margin of the shell ; their 

 interior lateral branches appear to touch, and thus give the appearance of uniting the two main 

 sinuses ; the lateral branches extend outward from the main sinus nearly to the edge of the shell, 

 while the interior lateral branches are crowded into the space between the main vascular sinuses 

 and the visceral area. The main vascular sinuses of the dorsal valve extend well forward and 

 curve inward toward the median line; their interior lateral branches fill the narrow space between 

 the vascular cavity and the main sinuses; no traces have been observed of the peripheral 

 branches of the vascular system of the dorsal valve. The parietal scar is shown more clearly 

 for the dorsal than for the ventral valve. In the former it extends about the space occupied by 

 the central scars, but it has not been traced outside of the main sinuses or in front of the 

 anterior lateral muscle scars. 



Observations. — I was greatly puzzled when studying Matthew's figures [1894, PI. XVI] of 

 "Leptoiolus grandis, Lingulella ? cuneata, and Lingula cf. hillingsiana." It seemed, after 

 extended study of the character and variation of the interior markings of Obolus and Lingulella, 

 that the three species should be referred to Lingulella and perhaps to one species. Doctor 

 Matthew very kindly sent me his material, including the type specimens of this species. At 

 first I was inclined to consider "Leptoholus grandis" as distinct from Lingulella, but on close 

 study it became more and more evident that the differences were such that a generic distinction 

 could not be based upon them. The anterior extension of the main vascular sinuses varies 

 both in form and degree with different species of Lingulella. This may be seen by comparing 

 Lingulella ampla (Owen), Lingulella acutangula (Roemer), etc. The position and size of the 

 visceral area and muscle scars of the dorsal valve are also subject to great variation, as may be 

 seen by comparing Lingulella acutangula, and L. ampla. 



AH of the material of Matthew's "Leptoholus grandis, Lingulella ? cuneata, and Lingula cf. 

 hiUingsiana" is from one locality and bed. It comprises a large number of shells on some 

 twenty-seven pieces of rock. I found that there was more or less distortion of the shells by 

 both vertical and lateral compression. Where the interior markings are well preserved the 

 shells can be at once referred to Lingulella grandis. It is only in shells that are distorted or a 

 little larger, or where the interior is imperfectly shown, that any doubt arises, and even in this 

 case no undoubted dorsal valve was found that could be referred to any other species than 

 L. grandis. 



The illustrations of " Lingulella f cuneata" [figs. 5a and 5b] and "Lingula cf. hillingsiana" 

 [figs. 6a and 6b] by Matthew [1894, PI. XVII are all of ventral valves, and the figures of "Leptololus 



