8 



BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



usual oval proloculum (1), followed by a closely coiled tubular cham- 

 ber (2) ; the second chamber may be directly compared to Comuspira, 

 and at this stage Opthalmidium has completed the developmental 

 characters of an adult Comuspira. The third chamber (3) intro- 

 duces several new characters. The first of these is seen in the length 

 of the chamber, which is between two-thirds and three-fourths of a 

 sinele coil. This characteristic chamber, while seen as a definite 

 stage in this genus, has not been noted as an adult character in any 

 known genus. With this characteristic length of chamber comes 

 another character seen in the tendency to lose the close-coiled con- 

 dition at the distal end of the chamber. Near the aperture the 

 chamber leaves the preceding chamber and takes a tangential direc- 

 tion, thus standing out from the origi- 

 nal direction of coiling. The fourth 

 chamber (4) has the same charac- 

 teristic length in most cases becom- 

 ing a little nearer the two- thirds of 

 a coil, being slightly shorter than the 

 preceding, chamber 3. Toward its 

 aperture it also tends to take a tan- 

 gential direction, so that its aper- 

 tural portion stands free from the 

 preceding coils. At its beginning this 

 chamber starts at some distance from 

 the inner coils due to the separation 

 of the apertural portion of the pre- 

 ceding chamber (3) from the rest of 

 the test. As a result there is a 

 space left which is filled in by a 

 thin plate like portion of shell. A 

 similar filling is seen where chamber 

 5 starts its growth. These more or 

 less triangular areas are shown by 

 the smaller dotted areas of the figure. Chamber 4 also adds 

 another really specific character, that of building a peripheral wing- 

 like shell growth about its own outer wall. Thus chamber 4 in- 

 troduces the specific character of a peripheral wing, although the 

 true generic characters are not yet attained. 



Chamber 5 initiates the adult characters as far as the genus is con- 

 cerned. This consists of a chamber making a half coil. In this 

 particular species it also loses the character of uncoiling at its aper- 

 tural end but has the wing-like growth on its own periphery. Fol- 

 lowing chambers keep to the character of developing a half coil and 

 aclose coiled condition throughout. 



fig. 0. — opthalmid1um inconstans h. b. 

 Brady, x Co (Adapted from Brady). 

 Young specimen viewed by transmitted 

 light, showing (1) proloculum, fol- 

 lowed by (2) a long cornuspiralike 

 second chamber, three and one-half 

 coils in lengtn, (3 and 4) chambers 

 three-fourths to two-thirds of a coil in 

 length and (5) the first adult ch ameer 

 one-half of a coil in length. dotted 

 portion shows tne flangelike carina. 



