566 MEMOIRS OF THE CARNEGIE MUSEUM. 



Hinge rarely with teeth, which, when present, are much reduced and consist 

 only of pseudocardinals or irregular teeth. Real laterals are never present. 



Muscle-scars on inside of shell rather variable. Generally the anterior re- 

 tractor-scar is united w'ith the adductor-scar, forming an upper continuation of 

 it (thus differing from the normal condition seen in the HyriincB). But in some 

 cases the retractor-scar is partially or entirely isolated. Anterior protractor-scar 

 quite variable, isolated from adductor-scar or contiguous with it, or even confluent 

 with it. The posterior scars are rather uniform, agreeing with the Hyriince, the 

 retractor-scar forming an upper process of the adductor-scar. Only in one case 

 {Anodontites enHifurmis), are these two scars widely separated. Dorsal muscle-scars 

 mostly absent; if (rarely) present, only one may be found, or (in Leila) a row of 

 them. (In the Hyriince several are always present.) 



The pallial line is mostly simple and parallel to the margin ; but in one genus 

 (Leila) it forms a shallow sinus posteriorly. This undoubtedly is connected with 

 the closing of the branchial opening in front, but unfortunately no soft parts of 

 this genus are at hand, so that particulars cannot be given. Very often the pris- 

 matic border on the inside of the margin of the shell is unusually wide. 



The ligamental sinus is comparatively large, larger than in the Hyriince; it 

 may be broad and deep, but not sharply triangular (Ihcringella), or deep and sharply 

 triangular (in the other genera). In Mycetopoda it is shallow, but with a sharp 

 lower angle. 



As to the characters of the soft parts see above (p. 457). But it is well to 

 point out here that the chief features in which this subfamily differs from the 

 Hyriinoi are found in the structure of the gills (text-fig. 3, /, o, p. 458) which have 

 well developed, solid septa, moderately closely set, running parallel to the gill- 

 filaments (PL XLVII, figs. 3, 4). In the female (PI. XLVII, figs. 36, 46; text-fig. 3i, 

 p. 458), the septa of the marsupial inner gill are stronger, but not distinctly more 

 crowded than in the non-marsupial gills, and have close to the outer lamina (primary 

 limb) a ridge on each side, projecting into the lumen of the water canal, incom- 

 pletely dividing the latter into two compartments (PI. XLVIII, figs. 6, 76, 8). 

 The inner compartment, towards the inner lamina, assumes, when charged, the 

 function of an ovisac, containing the eggs or embryos (PI. XLVHI, fig. 76), which 

 do not stick closely together, and this compartment expands to a certain degree, 

 the corresponding section of the septa stretching out, while the outer compartment 

 (close to the other lamina) retains its shape, and does not contain eggs, thus ap- 

 parently serving as a secondary water-tube. 



The size of the eggs is small, 0.07 to 0.09 mm. According to Von Ihering the 



