224 SYNOPTIC COLLECTION. 



In Terebra and Turritella we have illustrations of a 

 perfect spiral of many whorls without projecting orna- 

 mentation in the form of spikes or flutings. In Terebra 

 subulata Lam. (No. 472), the early whorls are nearly 

 colorless but those succeeding are marked by deep red 

 spots. Both the young and adult shells are smooth, not 

 having even the revolving lines and ridges seen in Turri- 

 tella (No. 473 ; in this shell the youngest specimen has 

 nineteen whorls and the one with the largest body whorl 

 only sixteen, showing that the youngest whorls are broken 

 off). The margin is entire in both genera. Cerithium 

 tuberosum Fabr. (No. 474), has the revolving lines of 

 Turritella and in addition the vertical ridges. The mar- 

 gin has a short, slightly recurved canal. 



Vermicularia begins its life with a tightly coiled shell 

 (see No. 475, V. spirata Phil.) that is similar to Turritella. 

 Living in the cavities of a sponge it needs to keep at the 

 surface of the growing animal in order to obtain food. 

 It succeeds in doing this by forming a loosely coiled shell 

 (No. 475) or in growing straight. We have here and in 

 Magilus similar conditions producing similar results, and 

 both are good illustrations of adaptation of structure to 

 habit. 



On the west coast of Florida, Vermetus lumbricalis, var. 

 nigricans Dall, forms rock-like masses, as shown in No. 

 476 (which, on account of its size, is placed at the back 

 of Section 8) . When in the water the tubes are erect. 

 The greater part of each tube is straight though some of 

 the tubes show a spiral structure at the smaller end. 



Gyrineum spinosum Lam. (No. 477), has a colorless, 

 smooth, snail-like spiral at the apex, the general appear- 

 ance of which is distinctively unlike the succeeding whorls. 

 The latter are somewhat flattened and have vertical ridges 

 or varices with intervening short knobs and spikes. Ac- 

 cording to Adams the shells that are armed with these 

 knobs are found in rocky places, while the smoother spec- 

 imens come from deep waters. 



