702 DEEP WATER MOLLUSKS AND BBACHIOPODS—DALL. voL.xvn. 



niable. None of them seems to have undergone segmentation. The 

 orifices of the genital glands are situated on the surface of the visceral 

 mass, close to but not coalescent with each other, a pair on each side 

 symmetrically above the opisthopodium. A large number of ova existed 

 in the suprabranchial chamber, embedded in a large mass of transpar- 

 ent jelly, the office of which may be surmised to be their retention in 

 the chamber during the ejeetion of water from the anal siphon. The 

 ovary is distributed rather sui^erficially anterior to and outside of the 

 nephridial mass. The ova are spherical, covered with a transparent 

 layer of epithelium distinctly pedunculated at the point where it sepa- 

 rates from the ovary, but which is soon lost. The eggs are relatively 

 large and perfectly visible to the naked eye. In the specimen the 

 contents had been hardened and whitened by the alcohol, but showed 

 no indications of segmentation. The jelly-like mass in which they 

 were embedded after leaving the ovary was very posterior, gathered in 

 and over the folds of the mantle lamina, chiefly on each side of the 

 opening of the anal si]3hon, and not at all over the dorsal surface of the 

 gills. Some of the jelly was taken out and put in a receptacle full of 

 water, where strong currents of water directed upon it with a small 

 syringe failed to dislodge the ova. This explains how, in species which 

 incubate the eggs in the anal chamber, they may be retained there 

 when the water in the chamber is exjielled, a matter which otherwise 

 would be something of a puzzled 



The differences between this genus and Euciroa and Verticordia are 

 sufficiently conspicuous. No doubt the relation is more close with 

 Lyonsiella. If the thick fleshy imperforate sej)tum of Verticordia is in 

 any way homologous with the reflected nephridial Ifimina, oi Ealicardia, 

 the relationship might be regarded as quite close. But the impres- 

 sion derived from the dissection of Verticordia acuticostata was that 

 the septum there is an extension of the siphonal septum. I have 

 endeavored without success hitherto to obtain another specimen of 

 Verticordia acuticostata for the purpose of making microtomic sections 

 which would probably settle the question. The most important result 

 of these comparisons at present is the light it throws on the muta- 

 bility of the breathing organs within relatively narrow systematic 

 limits. No one who has studied many of the recent and fossil Verti- 

 cordiidce can doubt that the three genera above mentioned are related, 

 and descended from the same ancestral stock. Yet we find in one an 

 archaic lamellar gill, in the second, a flcsliy septum and a degenerate 

 adnate gill, and in the third a gill wbicli, morphologically, is homo- 

 logous with the gill of Anaiinacea, but here is specialized in a Avay to 

 which no i)arallel is yet known, and with a septum partly made up of a 

 reflected nephridial lamina. Is the result of the presentation of these 

 facts to be the creation of three alleged "orders," or the recognition of 

 the mutability of an organ which never should have been used as a 

 sole basis for the higher systematic divisions? I believe the latter to 



