252 PROCEEDINGS OF THE ACADEMY OF 



ranged as usual in the genus(see ante, p. 222). The base of attach- 

 ment is shorter and stouter, the outer cusp of the laterals is larger 

 and on a shorter and stouter pedicle than in Cylindrella scseva^ 

 figured on page 222. There are no distinct marginals, the teeth 

 slightly and gradually changing in size as they pass off laterall}', 

 until in the extremes the two cutting points become of almost 

 equal size and the outer one ceases to be on a distinct pedicle ; 

 the base of attachment also in the extremes is almost square. 



This membrane is of interest, being the first described of the 

 section Gongylostoma, whose dentition was unknown to Messrs. 

 Crosse and Fischer. 



Cylindrella cyclostoma, Pfr. 



Mr. Arango to Mr. Bland. Lomas de Camoa, Cuba. 



Jaw as usual in the genus, with over 10 delicate ribs (see ante, 

 p. 222). 



Lingual membrane long and narrow, as usual in the genus. 

 Laterals 2, marginals about 8, these and centrals of same type as 

 those figured by Messrs. Fischer and Crosse (Journal de Conchy- 

 liologie, 2d s., X.), for the group Cylindrella, s. s., as in Cylin- 

 drella costata, pi. IV., fig. 2. 



The first marginal, however, surely is of same tj'pe as the late- 

 rals, though much smaller and somewhat modified in form. It 

 appears like a transition from the one to the other. 



Cylindrella (Thaiimasia) Humboldtiana, Pfr. 



Cuba. Mr. Arango to Mr. Bland. 



Lingual membrane long and narrow, as usual in the genus. 

 Teeth 8 — 1 — 8 of same type as figured by Messrs. Fischer and 

 Crosse for C. rosea (Journ. de Conch., XYIII, 1870, pi. lY. fig. 4). 



The species belongs, therefore, to their group Thaumasia. 



The jaw is as usual in the genus, with about 100 ribs. 



EXPLANATION OF THE PLATES. 



Plate XIX. 

 t. Testicle, 

 e. Epididymis. 

 ac. Accessory gland of last. 

 ov. Ovary. 

 ovid. Oviduct. 



