Clarke — -The Naples Fauna. 



II. CLYMENIN^E. 

 Family Cyrtoclymenidae, Hyatt. 



Genus Cyrtoclymenia (Giimbel), Hyatt. 



Gumbel, in 1863,* proposed a division of the Clymenice into groups, one 

 of which, the Cyrtoclymenia was intended to include those having a simply 

 curved lateral lobe. In completing the definition of the group and erecting 

 Gdmbel's divisions to the value of genera, Hyatt characterized the species of 

 Cyrtoclymenia as having depressed semi-lunar whorls (this is true only of the 

 earlier stages of the typical species, C. angustiseptata, Giimb.) and both ventral 

 saddles and lateral lobes rounded. 



Cyrtoclymenia neapolitana, Clarke. 



Under the name Clymenia neapolitana, the writer described, in 1892,* 

 the only species of Clymenia yet known from North American faunas. Since 

 the date of that description some additional specimens of the species have 

 been obtained which, though not adding materially to our knowledge of 

 the development history of the shell, have shown a more general diffusion 

 than was then known. The species has been found only as barite 

 replacements and as the most fully developed specimens are of comparatively 

 small size, we may still be in ignorance of the final stages in the growth of 

 the shell. The adult shell is laterally compressed to a moderate degree, the 

 outer whorl being comparatively narrow on the venter and subsagittate in 

 section. It is widely umbilioated, the number of whorls not exceeding six 

 in any observed specimen. The later whorls have a narrow, flattened periphery 

 which may be concave in final stages, and this flattening is well defined by 

 revolving lateral grooves. 



The ornamentation of the shell is highly characteristic ; the younger whorls 

 bear distant lamellar festoons which, when perfectly retained, rise into short, 

 tubular, disunited spines, abutting against the surface of the next later whorl. 

 These gradually disappear near the beginning of the fifth whorl and become 

 resolved into fine concentric growth lines. 



The development of the shell. Protoconch. The primitive shell is trans- 

 verse and ellipsoidal and though its lateral extremities project but little 

 from the margins of the first whorl, there is an evident contraction at the 

 neck of the protoconch which sets it off from the whorl. This form of the 



* Uaber Clymenia, ; Palaeootographica, vol. xi. 



* Amer. Joor Science, vol, xliii, pp. 57-62. 



