Hyatt.] 30 [May 20, 



is equal to Amm. armatus densinodus Quenst., and give both the 

 above described varieties the name of Deroceras Venarense. 



Deroceras nodogigas. 



This species really belongs to the series of which Amm. muticus 

 D'Orb. (Armatus densinodus Quenst.) is the first member, and not 

 to this genus at all. 



Platypleuroceras brevispina. 



This is the Natrix rotundus of Quenstedt. Sowerby's original is 

 really a variety of lattecosta, as well as the accompanying figure on 

 the same plate, but it seems best to accept Oppel's solution of the 

 difficulty, and cut the knot by applying the name to the Natrix rotun- 

 dus form. Natrix oblongus is entirely distinct in every respect. In 

 Prof. Fraas' collection there are two young specimens, undoubtedly 

 belonging to this species from Lias j3 Balingen. 



Amm. natrix oblongus Quenst. 



A careful examination of the young in Quenstedt's collection 

 shows them to be very distinct from the young of the preceding. 

 This resembles Bircliii until a late period, while Natrix oblongus, on 

 the other hand, is similar in the younger stages to the adult of Dero- 

 ceras densinodum\ the aspect and closeness of the pilae and truncated 

 spines, the form of the whorls and abdomen are precisely similar. 

 Finally, Quenstedt himself has remarked the similarity of the septa 

 in the adults of both forms. Here, as in many of the neighboring 

 forms, it is very interesting to observe the reversions caused by the 

 reappearance of the planicostan aspect of the abdomen in the 

 adults, accompanied by the loss of the armatoid tubercles. This 

 mode of development unites desinodum, nodogigas and this species, 

 into one genetic series. The name which should then be adopted is 

 that given by Oppel, Amm. submuticus. 



Cyeloceras natrix. 



This species is only separable from Cyeloceras bipunctatum by the 

 greater stoutness of the whorls and greater rotundity of the abdo- 

 men ; whether it should be separated from Natrix rotundus. or not, my 

 material does not permit me to determine. 



Cyeloceras bipunctatum. 



In the collections of Fraas, Quenstedt, and especially in one made 

 by Baron Schwartz, which I saw at Tubingen, it is easy to observe 

 that the old of bipunctatus becomes smooth, and possesses the same 

 form as the so-called Cycl. Masseanum. A specimen in the collec- 

 tion of Museum of Stuttgart is eleven and a half centimetres in 



