116 THE NAUTILUS. 



regular, but they do not form complete septa; an arrangement into 

 septa is indicated in so far as the connections stand in rows, but the 

 septa remain, so to speak, perforated, the holes in them being about 

 as long or slightly longer than the connections, and in the most cen- 

 tral part of the gill an alternating arrangement of adjacent rows is 

 noticed. Thus there are no distinct ovisacs, the latter forming rather 

 a network of communicating tubes. In the non-marsupial anterior 

 and posterior end of the inner gills the structure is similar to the 

 outer gill. The interlamellar connections of the marsupium are 

 rather thick, with thick epithelium, and when the marsupium is 

 charged they stretch out considerably. 



In the gravid female at hand the marsupium was filled with eggs 

 in various stages of development, which were rather free from each 

 other, not forming placentae. No fully developed larvae were seen. 



The following four characters of Hyria are of prime importance: 

 1. The closing of the anal opening above without forming a supra^. 

 anal. 2. The separation of the anal from the branchial opening by 

 a solid bridge, formed by the union of the mantle edges (diaphragm). 

 3. The contiguity of the inner gill with the inner palpus. 4. The 

 location of the marsupium in the inner gill alone. None of these 

 characters is found in any North American shell, but all four are 

 observed in Spatha. In addition, the palpi are more like Spatha in 

 their general shape, although they differ somewhat. 



The most important difference from Spatha consists of the structure 

 of the gills, chiefly the marsupium. Septa and water tubes are very 

 rudimentary in the non-marsupial gill, and the interrupted septa and 

 communicating water tubes of the marsupium are quite unique. In 

 this respect Hyria may be compared only with Margaritana, but in 

 the latter genus the interlamellar connections are quite irregular, and 

 do not show the slightest arrangement in rows parallel to the fila- 

 ments. Although there is a certain analogy to Margaritana there is 

 surely no homology. 



Another important difference is the restriction of the marsupium 

 to a part of the gill, while the complete connection of the inner 

 lamina of the inner gill with the abdominal sac is apparently of 

 minor value. 



The conclusion is that Hyria undoubtedly stands nearer to Spatha 

 than to any of the North American genera, and that it is as widely 



