116 MOLLUSC A. 



No. 464. Teuthopsis oblonga, Wagn. 



The osselet of this Dibrauchiate differs from that of the Squid in being nar- 

 rower in front and larger in the posterior part. The specimen is from the Litho- 

 graphic Limestone (Middle Oolite) at Solenhofen, Bavaria. 



Size, 6x3. Price, $0.60. 

 No. 465. Leptoteuthis gigas, Meyer. 



In this Calamary — the AcarithoteutMs gigantea, Munst. — the osselet is horny, 

 slightly convex, truncate in front and pointed behind. The specimen is from the 

 Lithographic Limestone (Middle Oolite), Solenhofen, Bavaria. 



Size, 18x4. Price, $1.50. 

 No. 466. Geoteuthis , Miinst. 



1 



An undescribed species. The osselet of this genus is characterized 



jpi^p*^ by a wide shaft, and is frequently accompanied by a well-preserved ink- 

 bag. The specimen shows the muscular tissues of the body, fins and 

 arms, with traces of the non-nacreous pen. It is from the Oxford Clay 

 (Middle Oolite), Christian Malford, England, and is in the private Geo- 

 logical Cabinet of Mr. Ward, Rochester. Size, 10 x 4. Price, $1.50. 



Order 2. — Tetrabranchiata. 



The Tetrabranchs have numerous hollow arms with retractile 

 tentacles, and a head retractile within an external shell. This shell is 

 a long cone, straight, folded or coiled, and divided into chambers by a 

 series of septa connected by a siphuncle which is central, ventral or dorsal. 

 The animal lives in the outer chamber, but holds vital conection with 

 the deserted rooms of its dwelling by means of the siphuncle. The 

 exact function of the siphuncle is still unknown. Its action cannot be 

 hydrostatic, for in the living Nautilus it is not dilatable. There is 

 only one living Tetrabranch — the Nautilus ; and this is one of the few 

 genera which have existed at every period of the world's history. This 

 Order came first and culminated as the more highly organized Cuttle- 

 fishes made their appearance. The families of each Order which are 

 most unlike ( Orthoceratidse and Belemnitidee) were respectively the first 

 developed. The four-gilled type began in the straight Orthoceras and 

 half-coiled Lituite of the Silurian, maximized in the complex Ammon- 

 ite of the Jurassic, and declined in the Cretaceous through the half 

 coiled forms and the straight Baculite. The straight Tetrabranchs must 

 have lived habitually in a nearly vertical position, while the discoidal 

 genera would also creep over the sea-bed with their air-chambers above 

 them. 



