Thd Genus Gyrotoma 19 



vertical growth lines are crossed by transverse lines, very delicate and usually dis- 

 continuous. Fissure oblique, 6 mm. in depth. The suture is covered by a narrow, 

 cord-like, irregular girdle somewhat lighter than the general body color. In a broken 

 place in this "hem"' the suture appears as deeply impressed or channelled. Color of 

 shell brownish-olive. The bands are deposits of coloring matter in the base of the 

 folds, sometimes coalescing so that for the eleven folds of the body whorl six bands 

 show in the aperture. Columella narrow, rounded from center to base, flattened 

 above the center and having a heavy callus at the fissure; white from center to base, 

 dull purple above. Aperture elliptical, with a distinct sinus below. Outer lip a 

 little crenulate, firm, broadly curving outward at the top and slightly inward at 

 the base. 



Operculum: Leaf-like, leathery, very dark red. Apex acute, base rounded; right 

 margin much more curved than the left. Whorls three, the first two tightly coiled 

 and close to the left margin and about i mm. from the base. The region, of the inner 

 whorls is excavated or crater-like. Radiating lines are of varying strength. Altitude 

 8 1-2 mm.; diameter 4 1-2 mm. 



Measurements: Altitude, 21 mm.; diameter, 12 mm. Aperture: Lowest part of 

 fissure to base, 10 1-2 mm. ; diameter, 4 1-4 mm. 



Type Locality : Coosa River, Fort William Shoals, Talladega County, Ala. 



Type in Museum of Zoology, University of Michigan; paratypes in Alabama Mu- 

 seum of Natural History. 



The affinities of this species are with G. lewisii (Lea). It differs in hav- 

 ing fewer and stouter folds, a more rounded body whorl, a deeper and 

 less oblique fissure and less shouldered aspect. While the question may 

 rise as to whether lezvisii is Goniohasis impressa Lea with a gyrotomoid 

 outer lip the position of hendersoni as a true Gyrotoma is not to be ques- 

 tioned. 



The fissure varies from 3^ mm. in depth in young shells to 6 mm. in 

 adults. As depth increases, the fissure becomes less oblique, or to put it 

 another way, more narrow. There is little variation in form, sculpture and 

 color. The bands are from five to ten, following no formula as in most 

 .other species of the genus. A young specimen of hendersoni is thin, suban- 

 gulate. The fissure is shallow, the suture rather indistinct, the bands many 

 and linear. Eight whorls are indicated for a full-grown specimen. 



The only locality known for this species is Fort William Shoals. Writing 

 from this place on July 17, 1914, jMr. Smith said: "On a reef just above 

 we got the regularly striate form which I have been callng G. lemisii, though 

 I am not at all sure. With it another which I take to be G. hahylonicum, 

 and a third form undescribed which I propose to name G. hendersoni ; it is 

 striate much like lezvisii, but has a square and moderately deep slit." In 

 September of the same year, Mr. Smith wrote: "The species which I 

 propose to name hendersoni is one of the most beautiful of the genus and 

 is apparently very constant." 



Group of Gyrotoma excisum 



Quadrate, bulbous, conic or elongate; the whorls smooth or with folds, 



often faintly plicate ; fissure ordinarily straight and as deep as 10 mm. ; 



girdle well-marked, though sometimes absent ; aperture elliptical; sinus 

 distinct ; bands : three in excisiwt, four in ladinatum. 



