790 SCIENTIFIC RECORD FOR 1885. 



A. Haswell, of S> dney. Aiisteilia, entitled " Studies on the Elasinobrancli 

 Skeleton." That naturalist examined the complete skeletons or skulls 

 of 17 species of Selachians, and has described the essential peculiarities 

 of the skull, visceral arches, shoulder g-irdle, pectoral fins, and pelvic 

 fins, as well as dorsal, anal, and caudal. The results of his examina- 

 tioiis are embodied in a summary in which he recapitulates the essential 

 characters of the various families and including groups. 



Professor Haswell recognizes for the plagios tomes generally two 

 orders, the Selachoidea and the Batoidei, which are characterized as 

 follows : 



The Selachoidei are distinguished in that " in the skull the post-orbi- 

 tal processes are usftally well developed ; the orbit is usually provided 

 with a cartilaginous floor formed of the basal plate ; there is always a 

 palato-basal articulation ; the rostrum usually consists of three bars 

 with large foramina at the base. There are a series of external branch- 

 ial arches ; the first branchial arch never articulates with the skull ; 

 the hyo-arch is supported by the hyo mandibular : the copula of the 

 hyoid has the form of a broad plate connected with its distal extremity. 

 The pectoral fin is not connected with the skull by means of an ant- 

 orbital cartilage ; the ventral portion of the pectoral arch is divided in the 

 middle by a more flexible portion into two lateral halves usually slightly 

 movable on each other, and the dorsal extremities do not articulate with 

 the spinal column. The pro- and meta-pterygia of the pectoral tin are 

 never greatly elongated, and usually have the form of relatively broad 

 plates." 



The Batoidei are recognized as an order contrasted with the Sel- 

 achoidei in the following terms: "The post-orbital processes are small 

 or absent ; the orbit is devoid of cartilaginous floor. There is no palato- 

 basal articulation. The rostrum, when present, is usually imperforate 

 at the base. There are no external branchial arches ; tlie first branchial 

 arch is sometimes directly connected by the hyo-mandibular with the 

 skull. When the hyoid arch is supported bj' the hyo-mandibular the 

 articulation takes place near the proximal extremity of the latter. The 

 ventral portion of the pectoral arch forms a continuous rigid bar ; the 

 <lorsal extremities of the arch are connected either with the spinal 

 column or with one another. The pro- and meta-pterygia of the pectoral 

 fins have the form of elongated narrow bars, and the mesoi)terygium 

 is insignificant. The anterior portion of the pectoral fin is connected 

 by a cartilage — the ant-orbital cartilage — with the ethmoidal region of 

 the skull." 



The Selachoidei, or sharks, are disintegrated into two " suborders," 

 named Palaeoselachii and Neoselachii. Professor Haswell considers 

 this grouping to "follow as a necessary conclusion from the researches 

 'Of Gegenbaur on the anatomy of the skull." The suboiders are distin- 

 guished by the following characters: 



In the Palaeoselachii " the occipital region of the skull is not so 

 sharply marked off from the spinal column as in other Elasmoranchii ; 



