HARPOCERAS SERPENTINUM. 438 



PI. XLIX, figs. 4 and 5, in which the shell is preserved and in the other specimen (figs. 6 

 and 7). Where the shell is absent all the sharp specific characters derived from the 

 straight sharp ribs and high prominent keel are much modified. 



The suture-line is well shown in both specimens ; the siphonal lobe is short and 

 narrow, with three digitations on its inner border ; the siphonal saddle, large and wide^ 

 is divided into two segments by a short accessory lobe which issues from the bottom of the 

 saddle ; the outer foliole has three lobes, and the inner is larger and terminates in four ; the 

 principal lateral lobe is large, and has a stout thick stem, with three lateral digitations on 

 each side, and one long terminal branch ; the lateral saddle is rather smaller than the 

 siphonal, and terminates in four folioles ; the inner lateral lobe is about one third the 

 size of the principal, with short side digitations ; the inner saddle is larger than the 

 lobe, and terminates in three small folioles ; the auxiliary lobes and saddles are very 

 smair(fig. 3). 



Affinities and Differences. — This species very much resembles Harp, striatulum. Sow., 

 its ribs, however, are more straight and sharp, and they possess obtuse tubercles near the 

 area, which are wanting in Ilarj}. striatulum, the whorls are also more flattened and square, 

 and the suture-line is more acute and intricate than in Harp, striatulum. This species 

 differs from Harp. Normanianum, with which it was formerly confused, in having simple, 

 straight, sharp, tuberculated ribs, all of which are undivided, and it has the keel much 

 higher, sharper, and more prominent. 



Locality and Stratigrapliical Position, — Harpoceras nitescens is found in the Marl- 

 stone beds at Hawsker, Staithes, Saltburn, and RockclifF, Yorkshire, where it is rare. In 

 Chipping Norton it occupies the same horizon, associated with several species of Mollusca 

 that are found in the Amal. margaritatus-ioViQ as Pecten (squivalvis, Monotis cygnipes. 

 Pinna folium, Modiola scalpricm, Cardium truncatum, Pholadomya ambigua, Trockus 

 imbricatus, Cryptcenia expansa^ Cryptcenia complanata, Belemnites Milleri, as reported to 

 me by Mr. Windus. 



Harpoceras serpentinum, Beinecke. PI. LVIII, figs. 1 — 3. 



Argonauta serpentinus, Reinecke. Naut. et Argon., p. 89, No. 2, pi. xiii, figs. 74, 



75, 1818. 

 — CECILIA, — Ibid., p. 90, No. 3, pi. xiii, figs. 7Q, 77, 1818. 



Ammonites serpentinus, Schlotheim. Die Petrefactenkunde, p. 64, No. 6, 1820. 



— capellinus, — Ibid., p. 65, No. 7, 1820. 



— Strangewaysi, Sowerby. Min. ConchoJ., vol. iii,p. 99, pi. 254, figs. 1 — 



3, 1821. 



— falcieer, — Ibid., vol. iii, p. 90, pi. 254, fig. 2, 1821. 



— MtJLGRAVitrs, Toung and Bird. Geol, Survey, York. Coast, p. 251, 



pi. xiii, fig. 8, 1822. 



56 



