68 SKENEID.E. 



H. atomus, examined by Dr. Lukis and Mr. Alder, has 

 only a single row of teeth, (as in some of the Pleuro- 

 branchiata and sea-slugs) , resembling miniature sharks' 

 teeth. The snout or head-lobe and position of the eyes 

 remind us of Akera bullata. Mr. Alder remarks that 

 " the animal is altogether of very simple structure, and 

 one of what Milne-Edwards calls degraded forms, occu- 

 pying a similar position among the Testacea to what 

 Limapontia does among the naked mollusks." I have 

 placed it provisionally in the Skenea family. 



I am still of opinion that this is a legitimate but di- 

 minutive descendant of the ancient genus Euomphalus. 

 From a dislike to offend the prejudices of palaeontolo- 

 gists, who treat the notion of reviving an " extinct " 

 genus as a scientific heresy, I have substituted another 

 name; but so notoriously imperfect is the geological 

 record that we ought not to be surprised if the pedigree 

 of Euomphalus cannot be traced down to the present 

 time. Homalogyra is an upper tertiary fossil; and 

 several species of flat-spired shells, which have been as- 

 signed to Solarium, occur in older formations, and may 

 be the missing links of the genealogical chain. The 

 description of Euomphalus in Sowerby's ' Mineral Con- 

 chology ' (vol. i. p. 97) is as follows : " An involute 

 compressed univalve ; spire depressed on the upper part, 

 beneath concave or largely umbilicate. Aperture mostly 

 angular/' The tiny living representative of the great 

 Trilobite family offers an analogy to the present case. 

 Has all creation dwindled, and are these its last days ? 

 Brown's genus Planaria was founded on young speci- 

 mens of Planorbis spirorbis and P. albus, which had 

 been washed down by a freshwater stream into the sea. 

 His genus Spira is characterized as ' ( nearly globular or 

 semiovate/' and comprised the fry of some common 



